[Request] Counter-attack script.

I'm looking for a script that can trigger counter attacks. I'd like to have one that'll let me set what kind of attack triggers the counter attack, and how the counter attack is performed. (Ex: Attacking an electric enemy with melee may trigger a shock counter attack, or attacking a gas enemy with fire may trigger it to explode, doing damage to the players as well as kill the enemy) Does anyone know of a script that will let me do this?