OK, I admit that I was fond of the idea of rules for striking a specific body part. Unfortunately, I grew up with the 2e-era rules that punished accuracy (the called shot). For 5th, I ported some of those ideas, but based the control on luck. These rules are based on a humanoid physiology as seen through the lens of game mechanics, rather than the physiology of injury.
If you wish to strike a specific body part, declare your target before you roll the attack. If you roll a natural 17 or higher and the attack succeeds, you strike the desired body part and the target creature must make a Constitution save (DC 8 + ability modifier*+ proficiency bonus) or suffer a special effect.
If you have combat superiority dice, you may spend a die before your attack roll and declare your target. If the attack hits, roll the superiority die and add its result to the damage dealt in addition to the given special effect.
*Use the ability score that was used to deliver the attack
**Choose which effect you would prefer to inflict upon the creature
Basing the Control on Damage
Thought about reducing the damage dealt as a control mechanism, but thought that would lead straight to "just deal hit point damage." In the 2e-era rules, the reduced accuracy of called shots meant that the rules were very seldom used even when they were in play in a given game. It was almost always better to whittle down a creature's hit points than risk a miss and potentially give a creature another round of actions.
If you wish to strike a specific body part, declare your target before you roll the attack. If you roll a natural 17 or higher and the attack succeeds, you strike the desired body part and the target creature must make a Constitution save (DC 8 + ability modifier*+ proficiency bonus) or suffer a special effect.
If you have combat superiority dice, you may spend a die before your attack roll and declare your target. If the attack hits, roll the superiority die and add its result to the damage dealt in addition to the given special effect.
Body Part | Effect |
Head | Stunned until beginning of your next turn OR Constitution save to maintain concentration made with disadvantage** |
Eye | Blinded until beginning of your next turn |
Ear | Deafened until beginning of your next turn |
Mouth/Throat | Cannot speak intelligibly until beginning of your next turn |
Hand/Arm | Creature drops whatever it was holding in targeted hand/arm |
Groin | Incapacitated until beginning of your next turn |
Legs/Knees/Feet | Speed Halved, Disadvantage on Dexterity saves until beginning of your next turn |
**Choose which effect you would prefer to inflict upon the creature
Basing the Control on Damage
Thought about reducing the damage dealt as a control mechanism, but thought that would lead straight to "just deal hit point damage." In the 2e-era rules, the reduced accuracy of called shots meant that the rules were very seldom used even when they were in play in a given game. It was almost always better to whittle down a creature's hit points than risk a miss and potentially give a creature another round of actions.