Make it expensive and not always worthwhile for special attacks like this
tl;dr: Game mechanics serve design purposes; the game itself is not a haphazard accumulation of specific mechanics. Your guiding principle should be how do I want the game to play out, with or without these special attacks, and how can the attacks fit that?. Game balance is strictly a DM's responsibility.
Newer players have asked me for things like this pretty regularly. The big issues I've encountered are:
- The game doesn't simulate those details very well outside of specific situations
It's often stated (correctly) that D&D is not a reality simulator. Its game mechanics are simplified abstractions of reality, and this both makes the game playable as well as making a lot of plausible actions difficult to translate into the game.
What does it mean for an enemy to be blinded? Presumably we're talking about the already-existing condition Blinded, which at a minimum grants advantage to every PC attack against the blinded enemy while also imposing disadvantage on every attack the enemy makes. That is a huge deal in game-mechanical terms, especially if it can be deployed for free and at will.
- Feats/spells/etc. often exist to do things like this
Status effects like Blinded do already exist in the game, and there are already ways to impose them on opponents. If a player has a Sorcerer PC and took the spell Blindness/Deafness, then a special talon attack that blinds foes steps on that player's choice of class and spell-- the choice of that spell becomes much less special, and in many cases is wasteful.
This is a serious problem, as PCs tend to specialize and letting other PCs encroach on those specializations for free can make a PC feel much less special and useful.
- Players have a film action hero-style idea of what things should work
Most of the time I see requests like this are players wanting to use movie-style approaches to make the game easier. My most common (and hated!) example is
I'd like to hit the guard in the head and knock them out
It would drain much of the tension and challenge from the game if this were possible, as standing guards would become largely useless and players would gain a new, easy way to avoid encounters without expending any limited in-game resources (like potions, spell slots, feats, and so on) or even a risk of failure. Also, it's totally unrealistic, but that's beside the point.
The game is already generally balanced in favor of players. This makes special attack effects less necessary-- how much of an advantage should blinding a foe grant to a PC that is expected to survive an additional seven battles before the next long rest?
None of that means you can't have special attack effects from called shots or creativity, but as DM you alone will have to balance things.
- Is this a specialized version of an attack, or a free bonus effect to
a regular attack?
- How often will such an attack succeed, and how will that success
impact the fight?
- Under what conditions would the special attack be worth attempting,
and when might it not be wise to try? How often will either circumstance come up?
- Can enemies attack this way too? How badly would it impede the
players if so? If not, why not?
- How will fights change when these special attack effects are applied,
and can combat still be fun, interesting, and challenging for your
I don't know a generic answer to these questions. Overall, I suggest the same approach I take to homebrewing game features in general:
- Establish a cost for making such an attempt, and think through how
fights will change due to the special attack effects to determine the
If it's just flavor for an otherwise normal attack which happens to confer the special effect, then the special attack is free and your players will probably never use a regular attack again. If, instead, it costs a reaction or bonus action to even make the attempt, suddenly the player has other factors to consider.
One approach I don't recommend is a bonus to the target's AC. It's an appealingly intuitive mechanic, but can be tricky. Higher AC means fewer hits, and that means that fights will tend to last longer, which will deplete PC resources (spell slots, HP, etc.). It also makes the benefit hard to set-- if you're accepting a 25% reduction in your likelihood to hit, you really need to get something useful in exchange for that extra risk.
That benefit is also highly variable. In a boss fight that will already probably take a long time to win, permanently blinding the boss confers an enormous advantage to the players for however long the fight lasts (the blindness won't just expire, as it would with a spell). In many lesser fights the blinding simply seems cool, but is really irrelevant to the outcome-- it might be more favorable to simply land more hits, as most fights rarely last long enough for the more hits/blindness effects tradeoff to be valuable.
- Consider gating these types of abilities behind a feat (or feats)
Taking a feat represents a high opportunity cost, since you could have taken a different feat or an ASI instead. That expense makes more spectacular effects more reasonable, though all balancing concerns within individual combats still exist. Think of it this way: if casually blinding an opponent is so easy for a PC to do, why would it not be the case that all combatants always do so? Feats are a decent way to square that circle.
- Keep it rare and roll-limited
Players declaring the result of an action is always problematic, and these sorts of requests tend to be in that category. "I want to rake at his eyes with my talons" is an interesting flavor description, while "I want to rake at his eyes with my talons and blind him" is a player dictating results beyond what player mechanics really allow.
PCs are always trying to hit enemies in combat, and the d20 and damage dice together describe how successful they are. A miss might be due to an enemy dodging, their armor deflecting a blow, or the attack simply not dealing any meaningful damage (a flesh wound!). A hit might be due to good maneuvering on the attacker's part or blundering on the target's part. A hit with a low damage roll might be a relatively ineffective strike, while high damage might be the opposite.
You can relegate the special attacks to dice roll results in the same way. If a PC can impose a special effect, like blinding, only on a critical hit, then that takes care of many of the "called shot" problems. And it works well with other limitations, such as requiring a feat first, trading off the bonus damage dice, or anything else. It's still possible, but not available to players at their whim.
When considering how to grant this player request, game out the mechanical consequences of any possible system and see if you think it supports a fun play experience for your players. You're always free to reverse an attempt that didn't work out the way you'd hoped, but understanding how the game will change (and how you and your players will respond to those changes) is the only way to keep the game from breaking.