Mechanics that disappoint you in every conceivable manner

[angelfromanotherpin]

Hrunting doesn't really belong on that list, because it's almost a perfect counter-example to your point. Beowulf is given it like right before he goes to confront Grendel's mother, and discards it in the middle of that fight for a better sword. Not only is it only associated with Beowulf for a relative instant of his career, he fucking upgrades from it.

Not to say that I don't agree with your point – Beowulf and Hrunting are an outlier in the larger pattern of signature weapons.

[Dogbert]

the idea of upgrading your magic items is kind of weird. I mean, how often do characters get new swords (for example) in fiction?

You say it like d&d was a game meant to emulate fiction.

Basically what you want requires either:

1) Changing d&d's objectives and method until basically ending up with a different game.

2) Playing another game.

[Drolyt]

Hrunting doesn't really belong on that list, because it's almost a perfect counter-example to your point. Beowulf is given it like right before he goes to confront Grendel's mother, and discards it in the middle of that fight for a better sword. Not only is it only associated with Beowulf for a relative instant of his career, he fucking upgrades from it.

Not to say that I don't agree with your point – Beowulf and Hrunting are an outlier in the larger pattern of signature weapons.

I kind of forgot about that, I was trying to list as many swords from as many different sources as possible. He actually has a third sword too. Still, even with three distinct swords he doesn't compare to D&D characters' constantly upgrading their magic item Christmas tree. Beowulf isn't the only one to upgrade his sword, King Arthur upgrades from Caliburn to Excalibur in some versions of the legend, the point is that in most stories this only happens once or twice at most. Or sometimes they have one sword and it upgrades, like the ten billion upgrades to Tessaiga in Inuyasha.

[Drolyt]

1) Changing d&d's objectives and method until basically ending up with a different game.

I'm not sure it would be that different of a game just because you didn't have a Diablo magic item system anymore, but either way I think that is the correct decision. The fact is that people want magic items to be special and awesome and the D&D magic item system completely fails at that. In fact it fails at pretty much everything, it is unbalanced and the economics of it are nonsensical among other things.

[Dogbert]

Also, let's not forget that fictional swords are protected by plot armor more often than not: Other than temporary inconveniences, they can't be lost or destroyed, so you'd need to include them as a "class feature" instead.

[Mord]

While Midnight and Ultimate Psionics have rules for Rayearth-like weapons that level up along with its owner, they're the exception, not the rule...

I think that that method is vastly superior to the current loot progression and it puzzles me why it remains exceptional. In addition to the flavor superiority, enchantment-by-deeds also corrects the economic imbalance between mages and nonmages. Stabby types need to spend piles of gp just to do their jobs, whereas mystics can spend their gp pile on enhancing the powers they already receive just for being at their current level.

Beowulf isn't the only one to upgrade his sword, King Arthur upgrades from Caliburn to Excalibur in some versions of the legend, the point is that in most stories this only happens once or twice at most. Or sometimes they have one sword and it upgrades, like the ten billion upgrades to Tessaiga in Inuyasha.

More examples to back up your point: Luke and Anakin Skywalker also upgrade their swords. For each of them, this marks a major transition point in their lives - from farmboy to Jedi and Jedi to Sith respectively. They definitely were not running around like Revan in KotOR constantly grubbing for +1% on their various equips.

Speaking of animu swords, let's not forget the entire cast of Bleach. Sword upgrades kind of became the driving concept of the story after the first arc (much to the detriment of overall quality IMO).

Also, let's not forget that fictional swords are protected by plot armor more often than not: Other than temporary inconveniences, they can't be lost or destroyed, so you'd need to include them as a "class feature" instead.

Archaeologist Class Feature: Indy's Hat.

[Josh_Kablack]

Is there a point in trying to endear a player to a +1 weapon he'll upgrade as soon as he's lvl 6?

No, but the idea of upgrading your magic items is kind of weird. I mean, how often do characters get new swords (for example) in fiction?.

Ffafhrd and the Grey Mouser explictly rename any swords they get to the name of their signature weapons.
Conan often loses or finds a sword in the course of a story- at least in the REH works.

[Laertes]

RPG characters tend to upgrade their equipment more than fictional characters, it's true. However, they also tend to upgrade themselves more than fictional characters. The rags-to-riches level climbing isn't really supported in heroic fantasy fiction. Locke Lamora, Aragorn, Conan and Beowulf don't really gain levels over the course of play. Arthurian characters do level, but it's in a limited badass-to-slightly-higher-grade-badass way, rather than dirt-farmer-to-godkilling-planar-creature way. The archetypical level 1 to level 20 climb is basically unsupported in literature.

Ironically, magical characters in fiction often do gain power dramatically over the course of play, but tend to be defined much less by their equipment.

As such, this might be a case where RPGs have to part ways from the fiction that inspired them.

[Schleiermacher]

Laertes, why do you say "RPGs", when your point applies pretty much exclusively to D&D?

M&M and Feng Shui characters don't advance, Shadowrun and GURPS characters go from "Badass" to "Somewhat more badass". WoD and Exalted characters are also in the "Badass to bigger badass" bracket, except White Wolf loves filling their settings with super-NPCs who have 10 million exp and superpowers which you will never get even if you nominally could.

[Username17]

If you upgraded your equipment at the rate that Vasilisa or Aladdin does, but you had as many stories told about you as a D&D character, you'd end your career with hundreds or thousands of magical doodads. It's pretty standard for a character in a one-off fairy story to get between two and five magical doodads.

Let's consider Perseus. He gets: a magic sack, a magic helmet, a magic sword, a magic shield, magic sandals, a magic horse, a magic man servant, and a magic medusa head. That is eight magic fucking things, and he only actually has five supernatural encounters. The entire adventures of Perseus could be done in a single evening of D&D (but would most likely be done over two nights, with the Gorgon quest and the Cetus quest being different). That rate of magic item accumulation is unsustainable for an ongoing game.

D&D doesn't posit a massively increased rate of magic item accumulation, it posits a massively slowed down rate of magic item accumulation as compared to the source material. It just also posits more stories with the same characters.

-Username17

[Laertes]

Laertes, why do you say "RPGs", when your point applies pretty much exclusively to D&D?

That's a fair criticism and I concede the point.

[Username17]

M&M and Feng Shui characters don't advance

Uh... no. M&M and Feng Shui games do not use the advancement system because the advancement systems of those games do not work. Those games are supposed to have characters that advance in them, but people who actually play the games usually cut those sections because they are ass.

Making character advancement systems for RPGs is actually quite difficult, because the rate people gain power in most source material is dramatically faster than what an ongoing RPG campaign can support. Peoples' desires cannot be fulfilled, because they want to go zero to hero in a single origin story, and then they want to continue that rate of advancement, and they want to game every week for five years straight. Exponential growth being what it is, something has gotta give.

And then there's the problem of divergence. Linear Warriors and Quadratic Wizards has been with us for a long time. And the way stories deal with the problem is by sidelining characters. In the Wheel of Time books, the character who goes on to be a sorcerer king jesus with a harem of bitches and building sized power foci just stops adventuring with the guy who is good with an axe and can talk to wolves. They stop being able to face the same threats, so they just stop facing the same threats. But in an RPG that shit doesn't fly. Each of the protagonists is the alter ego of one of the coauthors of the story and cannot be sidelined.

Character advancement for RPGs is actually really hard, and there are a lot of ways to fail at it. And games like Feng Shui and Mutants & Masterminds fail so hard at it that even people who like the games say that you're better off cutting the system entirely and just playing the game at a particular sweet spot until you grow tired of it and then playing something else.

-Username17

[Cyberzombie]

Character advancement for RPGs is actually really hard, and there are a lot of ways to fail at it. And games like Feng Shui and Mutants & Masterminds fail so hard at it that even people who like the games say that you're better off cutting the system entirely and just playing the game at a particular sweet spot until you grow tired of it and then playing something else.

What's the problem with the M&M advancement system?

[Username17]

Character advancement for RPGs is actually really hard, and there are a lot of ways to fail at it. And games like Feng Shui and Mutants & Masterminds fail so hard at it that even people who like the games say that you're better off cutting the system entirely and just playing the game at a particular sweet spot until you grow tired of it and then playing something else.

What's the problem with the M&M advancement system?

People who fuck around with the system more than I do can give you a better description of the specific failure points, but the short version is that the set of viable characters is wildly different at different power levels. So for example, if you want to be a Martian Manhunter style shapeshifting telepath, you can do that - but only with a certain minimum power level under your belt. If you start earlier and work your way up, you'll just suck ass all the time because the intermediate versions of that character concept don't have a lot of level appropriate things to do. On the flip side, if you have a lower level concept like Martial Arts Detective, you'll run out of things to spend points on and have to get yourself an expanded shtick (with gadgets or magic or something), and you'll start buying that shit up from the bottom, which means it won't be level appropriate for a long time. Essentially forcing you to crawl on your tongue through being a fail character for a considerable period while you rework yourself into a character whose phlebtonium abilities are good enough to handle the level they have been raised to.

So a lot of people suggest just picking a power level that supports the character concepts the players want to use and then just ignoring the character advancement rules altogether. To the point that Schleiermacher made the generalization that "M&M characters don't advance." Forgetting that that was a house rule designed to address a perceived failing in the rules.

-Username17

[momothefiddler]

I admit I didn't spend as much time reading rulebooks when I was playing M&M as I do now, but until just now I honestly didn't even know advancement was supposed to be a thing, outside of plot points. The only time I had a character advance was in one game where we hit a major plot point and the MC bumped us up a few Power Levels and let us rework the characters within the approximate concept.

Which is another example of people discarding the advancement system altogether, I guess.

[Lago PARANOIA]

Peoples' desires cannot be fulfilled, because they want to go zero to hero in a single origin story, and then they want to continue that rate of advancement, and they want to game every week for five years straight. Exponential growth being what it is, something has gotta give.

Looking at your trichotomy, I'd say the biggest problem is 'game every week for five years straight'. That's not just a game design problem, that's a metafictional problem.

See, if you're proposing a story in which the reset button isn't continually pressed, shit changes. People get new allies, people discover new tools, people get more superpowers, whatever. If you have a finite number of stories then you can control the rate of plot advancement enough so that shit doesn't get out of hand by the time the campaign ends. But a character lasting 250 or even 50 stories where three stories is longer than a television season? Not a chance in hell. Dragonball and One Piece's shit didn't get out of control because Toriyama and Eiichiro are bad writers; it's a limitation of their medium and story design paradigm.

And honestly, I have no idea how to solve this problem. All you can really do is delay perdition. That said, you do have a few tools in your trunk to deal with this, with varying degrees of success and desirability.

[*] Introduce various reset buttons in the game. Magical items run out of charges with no guaranteed way to replay them, wight ambushes drain your level, whatever. Note that character permadeath is an extremely ineffective reset button unless you have a TPK, in which case you don't really have a continuing story.
[*] Try to hook peoples' attention with various minigames. If you can get your characters interested in running a business or directing troops into battle, you can freeze character advancement while still continuing their stories.
[*] Coax your players into letting another group of characters have the spotlight at times. If you have a Game of Thrones thing going where sometimes the players control a different group of PCs in the same campaign setting, you can continue the story while freezing advancement.
[*] Lean on character advancement that retools a character's superpowers rather than giving them straight horizontal or vertical advancement. For an extreme example, imagine if Harry Potter, instead of getting more spells, lost his ability to do magic and instead picked up the Millenium Puzzle and a deck of magic playing cards. Then after that got stale, his latent mutant powers activated after the Puzzle got destroyed and he became a super-scientist.

[Nebuchadnezzar]

What's the problem with the M&M advancement system?

The general requirement of meeting Power Level limits disincentivizes the horizontal growth encouraged by the default incremental advancement schedule. This leads to problematic behavior like players racking up tons of Alternate Effects, since that's usually the easiest way to shove a point or two into a complicated power, and after a certain point the most efficient use thereof.

Generally the best way to handle changes in Power Level is to save up experience and simply recreate the character at the new level. Perhaps one throws in a the odd extra point after a session. limited to fluff like Features and Expertise (pop culture). Alternatively, one can treat the effective PL of a game as 1 higher than current points would indicate, allowing a gradual hitting of caps throughout the level. Since that tends to lead to jacked up arrays (to use the 2E term) and people reserving points it's easiest to just replace advancement with occasional rebuilding. Precipitating contrivances like radiation exposure and bathing in magic pools are recommended, but just calling it a reboot seems equally appropriate.

[Insomniac]

In a spell slot system predicated on 2 to 4 battles per day, there has never been balance between those classes that expend resources to do amazing things and the classes that get to do it "all day long."

I think the Warlock in 3.5 Dungeons and Dragons is an underpowered botch job. Classes without expendable resources, primarily magic, always lag the classes that have it. This was true in Dungeons and Dragons but Pathfinder absolutely codified this.

I don't know how a d20 system is supposed to do magic. It always devolves
to me into If You Ain't Casting, You Ain't Shit.

Also, any efforts to give martial classes any sort of expendable resource
pool is loathed as "weeaboo" and "you want fighters to be magical!"

After 7th level in a d20 system, I feel like a complete chump if I am playing something that can't cast a spell.

[Seerow]

In the Wheel of Time books, the character who goes on to be a sorcerer king jesus with a harem of bitches and building sized power foci just stops adventuring with the guy who is good with an axe and can talk to wolves

Even then, Wolf Talking Dude eventually takes a level in badass just before all of the crew meets back up for the big finale, and gets to play Neo in the Dream World/Matrix equivalent, and playing as Sorcerer Jesus's guard dog in that realm during the whole final confrontation.

[Josh_Kablack]

Looking at your trichotomy, I'd say the biggest problem is 'game every week for five years straight'. That's not just a game design problem, that's a metafictional problem.

I'm not so sure that's the biggest issue in actual play. The majority of games I have personally run and played in are still all "Two Semesters or less" range. Yeah, there were a couple really memorable 3+ year campaigns, but those are a drastic minority. And yeah, sometimes a semester long game is merely 10 weekly sessions of 3 hours each and other times it's 6 hours damn near every night in the dorm's common room with whoever is around.

But overall, multiyear campaigns are a tiny minority of the games that actually happen. It's really probably fine to set up a game that reaches max advancement after somewhere between 20 and 100 sessions as the default rate.

[Dean]

A story doesn't have to hit 250 sessions to start running into the problems being discussed here. There's very few fantasy stories that cover as much ground as a normal D&D group would in just a few months of gaming, even very long stories like LoTR. This is because the density of D&D storytelling is unusually high. Because the audience and the main characters are the same people it means there is no time spent on segments of the story that don't move it forward. There aren't 45 campfire scenes and ten chatting in the woods scenes and scenes where a character analyzes their own self doubts and debates whether they really can go through all of this. It's just scene after scene of the party moving forward, moving towards their goals, accomplishing objectives. The amount of story that progresses in one semester for a D&D group would take at least 2 movie trilogy's to cover.

[Wiseman]

Infernum's mass combat system. I have yet to see a more complex, confusing, and downright unplayable system than this. You end up with units with thousands of hit points and dealing piddly 1d8+6 damage. Each round is supposed to simulate 5 hours of combat.

Here's a sample.

Haimon Legionnaire
(3rd level Damned)
Medium Damned
Progressions: Good Hit Points and Base
Attack Bonus, Average Skills and Feats, Poor
Saves
Hit Dice: 3d12+6 (25 hp)
Initiative: +1
Speed: 25 ft.
Armour Class: 21 (+1 Dex, +2 natural, +5
chain, +2 shield, +2 helmet), touch 11, fl atfooted
20
Base Attack/Grapple: +3/+5
Attack: Spear +6 melee (1d8+4) or javelin
+4 ranged (1d6+2)
Full Attack: Spear +6 melee (1d8+4) or
javelin +4 ranged (1d6+2)
Space/Reach: 5 ft./5 ft.
Saves: Fort +5, Ref +2, Will +2
Abilities: Str 14, Dex 13, Con 15, Int 8, Wis
12, Cha 10
Skills: Disguise +2, Escape Artist +3, Listen
+7, Spot +7, Warcraft +5
Feats: Martial Weapons Profi ciency, Plasmic
Body, Weapon Focus (spear), Weapon
Specialisation (spear)
Corruption: 15
Challenge Rating: 3
Equipment: Chain mail, heavy shield, spear,
helmet, shortsword, two javelins
Determining the ability scores for a legion of
these warriors is as follows:
Size: These damned are deployed in cohorts
(ten cohorts to a legion), which are composed
of around 1,000 troops. This means the unit
size is Huge.
Average Level: The average level is three
(there will be higher or lower-level damned in
the unit, but they will average out at three. The
cohort commander will probably be a special
character. Unit hit points are the average level
+ 2 (damned) x the number of damned. This
works out at a massive 5,000 hit points. The
Threshold value shows at what point the unit
will have to make a Cohesion check. In the
case of the Haimon Legion, this is when they
are reduced to 3,750, 2,500 and 1,250 hit
points.
Rating: Haimon legionnaires are Veterans,
giving them a +2 bonus to their attack and
damage rolls, saving throws and damage
thresholds.
Armour Class: This is taken straight from
the character scale, modifi ed by the unit’s
Size modifier; the legion has AC 21, –4, for
a total of 17.
Attack: This is based on the character’s
attack, plus the unit’s Veteran status, for a
final attack of +8.
Damage: Again, this is based on the character
scale damage plus the rating modifi er, for a
damage of 1d8+6. Furthermore, if the unit
Encircles a foe, it will do at least 1d8+6+4
(Huge size) and will probably be able to fl ank
or rear attack to double or triple its damage.
Saving Throws: As per the character, plus its
rating modifi er, for Fortitude +7, Refl ex +4,
Will +4.
Warcraft: The default Warcraft score for this
unit is 5 (base) +2 (rating) –4 (size), for a fi nal
score of +3. However, the cohort is lead by
a 12th level damned with a Warcraft score of
+15, so the fi nal rating is a mighty +17.
The cohort ends up looking like this on the
battlefield:
Huge Veteran Damned Unit
Level 3 (5,000 hp)
Threshold: 3,750/2,500/1,250
Movement: 2.5
AC: 17
Attack: Spear +8 (1d8+6)
Saves: Fortitude +7, Refl ex +4, Will +4
Warcraft: +17
here are some more units
Sample Armies
The units listed here are some of the more typical
or more famous units of the Infernum.

Astyanath Joyous Legion
Medium Crack Malcubus Unit (250 demons)
Level 15 (4,000 hp)
Threshold: 3,000/2,000/1,000
Movement: 3
AC: 20
Attack: +20 melee (Claw 1d8+11) or Bile Rifl e
+21 ranged (1d4+6)
Warcraft: +24
Special Abilities: Confuse, Joyous – in any round
when the unit is damaged, it gains a +2 bonus to
attacks and damage until its next round).
The infamous Joyous Legion are trained to love
pain, and become more dangerous when injured.
The Astyanath regularly attack their own forces to
prepare them for battle. The Joyous Legion are a
terrifying foe, as the demons drag themselves across
the battlefi eld to impale themselves ecstatically on
pikes and barbed wire.

Bori Warriors
Small Elite Mortal Unit (100 mortals)
Level 10 (1,000 hp)
Threshold: 750/500/250
Movement: 3
AC: 21
Attack: +15 melee (Two-handed sword 2d6+10)
Saves: Fortitude +5, Refl ex +9, Will+9
Warcraft: +16
Special Abilities: Boost, Rage
The mighty Sons of Bor are few in number, but
every one of them is a magnifi cent fi ghter. Their
war-cries strike fear even into the hearts of
demons, for the Bori are trained to kill
without mercy or hesitation.
Branded Raiders
Tiny Average Mortal Unit (25 mortals)
Level 3 (75 hp)
Threshold: 54/36/18
Movement: 3
AC: 16
Attack: +3 melee (Sword 1d8+1) or Shortbow +3
ranged (1d6+1)
Saves: Fortitude +1, Refl ex +4, Will+4
Warcraft: +5
Special Abilities: Boost
Raiders like this trouble many demon domains.
While they are not especially tough in battle, they
melt away into the shadows of the Pit like ghosts
after freeing slaves and damned from bondage.
Carthenay Guards
Medium Average Beast Unit (300 demons)
Level 5 (1,800 hp)
Threshold: 1,350/900/450
Movement: 2
AC: 20
Attack: +5 melee (Mace 1d6+1) or Bile Rifl e
+5 ranged (1d6+1)
Saves: Fortitude +5, Refl ex +2, Will+2
Warcraft: +8
Special Abilities: None.

These guards of House Carthenay protect the
fortresses and vaults of the Miserly House. Despite
the Carthenay’s reputation for not spending money,
these guards are well armed and armoured.
Damned Rabble
Gargantuan Rabble Damned Unit (5000
damned)
Level 1 (15,000 hp)
Threshold: 11,250/7,500/3,750
Movement: 2
AC: 6
Attack: +0 melee (Club 1d4)
Saves: Fortitude +2, Refl ex +0, Will+0
Warcraft: +0
Special Abilities: None.
Massive units of damned like this are used as
cannon fodder in the wars of the Infernum.
Free City Levy
Large Untrained Demon Unit (500 demons)
Level 2 (1,000 hp)
Threshold: 750/500/250
Movement: 3
AC: 13
Attack: +0 melee (Claw 1d8–1)
Saves: Fortitude –1, Refl ex –3, Will –3
Warcraft: +0
Special Abilities: None.
Glabretchi Scorchers
Small Veteran Slaver Unit (100 demons)
Level 6 (600 hp)
Threshold: 450/300/150
Movement: 3
AC: 22
Attack: +9 melee (Claw 1d8+5) or hellcannon +8
(varies)
Saves: Fortitude +11, Refl ex +6, Will+6
Warcraft: +11
Special Abilities: Hellfi re, DR2/fi re, Pestilence
The Glabretchi rely on aggressive troops like this
when pushing outside their estates. A blast of
hellfi re from their cannons will deal with the most
resilient foe – or with enemies immune to Putrid
diseases.
Lictat Brigade
Small Green Stalker Unit (100 demons)
Level 2 (200 hp)
Threshold: 150/100/50
Movement: 3
AC: 14
Attack: +1 melee (Claw 1d8+1) or Bile Rifl e +1
ranged (1d4+1)
Saves: Fortitude +2, Refl ex +2, Will+0
Warcraft: +5
Special Abilities: None.
The Lictat estates are vulnerable, as they are
defended by relatively weak and unarmed troops
like these ones. Their main advantage is their
knowledge of the terrain of the Second Circle.
Oblurott Cavalry
Medium Veteran Slaver Unit (250 demons)
Level 5 (1,750 hp)
Threshold: 1,320/880/440
Movement: 5
AC: 22
Attack: +8 melee (Lance 1d10+5)
Saves: Fortitude +7, Refl ex +7, Will+4
Warcraft: +10
Special Abilities: Agile, DR5/Slashing
These fast-moving spawn-riders carry their
bloated demon masters into battle. Cavalry like
this shattered the Sturrach defenders in the Fourth
Circle.
Sturrach Slaughterers
Medium Elite Hulk Unit (250 demons)
Level 15 (4,500 hp)
Threshold: 3,375/2,250/1,125
Movement: 2
AC: 28
Attack: +24 melee (Claw 2d6+14) or hellfi re +24
ranged (varies)
Saves: Fortitude +13, Refl ex +13, Will+9
Warcraft: +19
Special Abilities: Hellfire
One of the most feared units in the whole Pit, the
Slaughterers of Count Zarov are unstoppable in
battle.

[GâtFromKI]

Magic items should be special, and nothing is less "special" than having a bonus you're supposed to have anyway.

Grrr....

Every time I hear a GM say "magic items should be special", it turns out to be code for "my players should be falling over themselves with gratitude every time they find a Helm of Underwater Action". I'll give you the benefit of the doubt and assume that's not what you're trying to say, though.

Well, yes and no.

First of all, I want that the player don't need anything, be it a helm of underwater action or a +1 sword. If they are supposed to fight incorporeal creatures, they should have class abilities allowing that. The whole game should be functional and balanced without any magic item.

Then, every magic item should allow them to do things they aren't supposed to do (or before the level they are supposed to do it). The thing they do can be useless or great, anyway they don't need it. So I can give them what I want, and there is no problem if they decide to leave it here, to burn it, or to keep it. I don't have to recompute their wealth if they decide to keep some useless dump instead of selling it, I don't have to check if I give enough +2 weapon and enough cape of resistance.

[Lago PARANOIA]

But overall, multiyear campaigns are a tiny minority of the games that actually happen.

Okay, and? The vast majority of people are never going to win big on the lottery or slots or craps tables or whatever. Nonetheless, players will become demotivated by hearing enough tales of winners getting fucked over by the rewards committee or tax collection agencies or whatever.

[Kaelik]

Magic items should be special, and nothing is less "special" than having a bonus you're supposed to have anyway.

Grrr....

Every time I hear a GM say "magic items should be special", it turns out to be code for "my players should be falling over themselves with gratitude every time they find a Helm of Underwater Action". I'll give you the benefit of the doubt and assume that's not what you're trying to say, though.

Well, yes and no.

First of all, I want that the player don't need anything, be it a helm of underwater action or a +1 sword. If they are supposed to fight incorporeal creatures, they should have class abilities allowing that. The whole game should be functional and balanced without any magic item.

Then, every magic item should allow them to do things they aren't supposed to do (or before the level they are supposed to do it). The thing they do can be useless or great, anyway they don't need it. So I can give them what I want, and there is no problem if they decide to leave it here, to burn it, or to keep it. I don't have to recompute their wealth if they decide to keep some useless dump instead of selling it, I don't have to check if I give enough +2 weapon and enough cape of resistance.

That is dumb and you should feel dumb. What the players need is what they need to beat level appropriate challenges basically 100% of the time. If they have that without any magic items, and then you give them magic items, then they are just equivalent to a higher level character. At which point you can either: 1) Have them challenged by the same shit they would fight without the magic item and have it be trivially easy. 2) Have them be challenged by shit they need the magic item to beat, and then the magic item becomes mandatory.

There is no option 3 where they have magic items that give them new abilities that are not either making everything too easy, or required.