Puddles
Adventurer
This sounds like a great idea, especially for large tables where it takes a while for players to get their turn. I would key it off reactions. Doing so, means the player/DM has a choice to make. They can use their reaction when an enemy misses an attack, but of course doing so would mean they couldn’t make other reaction such as opportunity attacks until their next turn.
I would have 2 different reactions, 1 to counter a missed melee attack, and 1 to close the distance from a missed ranged attack. I would start with the following:
Counter
When a melee attack misses, the target creature can use its reaction to counter. If it does so, the attacking creature takes 1d4 bludgeoning damage.
Close Ground
When a ranged attack misses, the target creature can use its reaction to close ground. If it does so, the target creature can move up to 5ft but must finish that move closer to the attacking creature.
I would have 2 different reactions, 1 to counter a missed melee attack, and 1 to close the distance from a missed ranged attack. I would start with the following:
Counter
When a melee attack misses, the target creature can use its reaction to counter. If it does so, the attacking creature takes 1d4 bludgeoning damage.
Close Ground
When a ranged attack misses, the target creature can use its reaction to close ground. If it does so, the target creature can move up to 5ft but must finish that move closer to the attacking creature.