Press X to Smash Into a Bloody Pulp When D&D was first published, people flocked to it out of a desire to play out their Lord of the Rings and Princess of Mars fanfic. As time went on, movies such as the Star Wars trilogy began to drive it (ok, probably not that much time. Star Wars came out in the same decade as D&D).
But honestly? Now video games like Legend of Zelda and God of War are driving just as much interest in RPGs as anything else.
I'm aware of a handful of attempts to do finishing moves and similar shit in tabletop games, and the mook rules that are getting to be common in newer fantasy games seems to be intended to fulfill a similar role.
In D&D specifically, there's a maneuver in Book of 9 Swords that's literally called Finishing Move, which does very little unless the target is below half hp. In a third party Totally Edgy line of adventure modules (Goodman Games' Wicked Fantasy Factory), there's a tack on rule that gives all adventurers a finishing move, which requires an attack roll, and beating the target's remaining hp on a (half level)d6 roll. If you pull it off, you get some bonus XP. Coup de graces can be considered finishing moves as well, but don't quite fit the semantic.
And then there's various mook/minion rules.
Basically, every existing rule of finishing moves, that I'm aware of, is fucking shit.
Finishing moves, in their various source material, are things you use against an opponent that has been weakened to the point that the user has pretty much already won. They are fun, flashy, and, perhaps most notably for tabletop, quicker than slugging out the last bit of combat. I guess in some video games a "finisher" can actually be done at any time, but... we're going to ignore that.
When You Can Finish An Opponent
Personally, my main inspiration for this whole thing is stuff like God of War and Darksiders. Once you beat on an enemy enough, you get a little indicator above their head telling you that you can finish them off with an action command. In God of War, finishing an opponent this way gives you a little health, some mana (Rage), that sort of thing. In Darksiders, you just get mana (Wrath), because... iunno. Health is more scarce in Darksiders. Whatever.
Other sources of Finisher Moves are fighting games, like Mortal Kombat, where, again, you use a Fatality move when your opponent is already beaten.
So, a finisher move should be something you use when you've already won, and further slugging it out is basically a formality. And the more formidable you are, the more slugging you can consider a formality. So higher level characters should be able to use finishers on more powerful opponents. HP, and hp relative to another measure, is probably the best way to do this. Maybe comparing hp to a couple things, so, say, a target with equal or fewer hp than it has HD is on the ropes and can be affected by a finishing move, and a target with equal or fewer hp than you have HD is just so weak compared to you that it's nothing more than a speed bump.
What A Finisher Does
At it's most basic, a Finisher should finish an opponent. This means, at least, that we are straight discarding the Goodman Games Wicked Fantasy Factory Finishing Move rules out of hand, because "Roll to hit, then roll some d6s to see if your successful hit actually takes them out" is bullshit. Finishing Moves are supposed to be awesome, but also, they should be quicker than slugging it out.
Bare minimum, a Finishing Move should autohit and autokill. Your opponent is either so bloodied that a stiff breeze will take them out, or so weak you can kill them by spitting on them, you should be able to just straight choke slam them into the dirt. The action this should take is debatable. A lot of video games depict finishing moves on the order of full round actions. But if a finisher is a full round action, then there needs to be something to make up for the fact that you're exposing yourself to other enemies that may not be as injured, and, at higher levels, you're spending a full round to take out one enemy when you could be attacking at least two. We're going to say that a Finishing Move is a Full Round Action, but you can take a single Move Action as part of it (which means you can't perform a finisher if you're limited in your actions in any way), and when you Finish an opponent you get some hp back, and if you use spell points (or, rather, Power Points), you get some of those back. We'll also say you can recover daily uses, but only 1 daily use per encounter (so you can't refill your daily rages by picking a fight with kobolds and Finishing them one by one). We'll say you get to roll the opponent's hit die type, and regain that much hp, and if you have any kind of spell points, that many of those.
What A Finisher Is
When you use a Finishing Move, you perform some special action, that's within the plausible range of your abilities, to destroy the opponent in a particularly flashy way. You use the time that would be spent rolling and adding and comparing numbers for a trivial formality to instead feel awesome saying how you cleave the kobold in half or whatever. A Finisher can, and should, invoke your class or racial combat abilities, but does not consume uses of them, nor does it need to follow the normal rules for such. So a wizard who specializes in fire magic can say they engulf the cannibal halfling in a burst of flame from their dick, without spending a spell slot to do so, and a rogue can stab the cannibal in the dick even though they're in full view and no one's flanking the cannibal halfling.
Finish It
So lets look at this idea with some actual hypothetical numbers.
We'll say the opponent is a kobold to start with. A kobold warrior has 4hp on average, and 1 HD. Honestly, it's entirely within the realm of possibility that even a first level character can drop it in a single hit, there's no real reason to use a finisher, even when the kobold is dropped to 1 hp, except for that healing. If the kobold is left at 1 hp because your buddy rolled bad or something, you can use your finisher, saying you charge at the kobold and stomp its chest in, healing 1d8 hp and recovering 1d8 power points (or whatever). At sixth level, you're still very likely to be able to drop a kobold in one hit, and you're going to be encountering them in sufficient numbers that the full round action to finish one might actually be a deterrent when you could be attacking two regularly. But, maybe you could use that Cure Light, or that recovered Daily use, or you've just been rolling shit and would rather autokill the things than risk missing pitifully. So your sixth level character who gets ambushed by five kobolds can just straight up spend five turns stomping their heads in, or immolating them with dick fire, or whatever. And honestly, it can be glossed over with just a few rolls to see if the kobolds do enough damage to off set your healing, if anyone really cares.
Let's look at another example, a succubus. It's CR 7, so it's a reasonable challenge for a sixth level party, that should give them some trouble. A succubus has 6 HD, and, on average, 33 hp. If the succubus is dropped to 6 hp, but not taken out, you can use your finisher on her, and you'll heal a d8 of HP, and recover a d8 of spell points or a daily use. And honestly, against a succubus, the trade off between two normal attacks and an auto kill is way more reasonable.
Feats, Abilities and Finishers
In general, your capabilities just give you license to fluff your finisher, but some abilities should actually improve your finishers. Like, if you have Whirlwind Attack, there is literally no reason you shouldn't be able to incorporate that into your finisher to allow you to take out multiple viable targets at once. If you have Cleave, I'm totally ok with you Finishing two viable targets, and if you have Great Cleave, and you've got multiple Finisher targets, I see no reason you shouldn't be able to mow through them like the little pest opponents that exist to be stomped in a single Action Command in Darksiders.
This is a brainstorm, and I'm betting there are places it could be improved. The numbers are entirely arbitrary first thoughts.
