While running a session, I found that some of the players would like to "call shots".
Now while I don't want to allow "crit on desire" by always aiming for the head/eyes/etc., I was thinking about allowing it on a natural 20 – it's already guaranteed to hit & also do critical damage (most of the time), so what would be the effect of allowing this, assuming that the extra damage from "hitting in the head" would be the same as the normal crit bonus? This would be a fluff-only with no other effect besides the normal critical damage.
Has anyone tried running something similar to this? Does anyone see potential issues or unintended consequences? I'm looking at it as a way to allow the "fluff" without really changing the mechanics of it at all.
Related question: Aiming at specific body parts
Best Answer
As long as the crit is unchanged, then it is balanced.
If nothing is different besides the narration, then by definition the mechanics of the game remain balanced, at least to a first approximation.
Crits are meant to represent great successes in the midst of combat, so they are a nice opportunity for you or the player to add some narrative flair to the combat.
Beware of extreme called shots.
There are some called shots that simply cannot be successful without any mechanical implications. Consider these examples, where a player crits and wants the called shot to be: a decapitation with a greatsword; an arrow in the enemy's only eye; a strike that cripples a wing.
These called shots are admittedly extreme, but nonetheless it's clear that if they are successful they must come with unbalancing consequences: instant death, permament blindness, and loss of flight respectively.
Your premise is that such consequences do not occur, so your narration will have to undermine called shot like those to explain why the enemy only takes damage. The problem is that those called shots now feel like relative failures instead of unequivocal successes, because the player hoped for something more besides damage.
You have to manage your player's expectations
"Called shots" is not the term I would use to manage such expectations, because the default assumption is that called shots can include extra effects besides damage. Instead, just ask "Why don't you describe this crit?" or "How do you want me to describe this crit?". Questions like these provide just as much opportunity for flair and narration, without any of the expectations of a called shot.