Shellshock (TMC-025) [Commander: Teenage Mutant Ninja Turtles]

For each opponent, choose up to one target creature that player controls.
Shellshock deals X damage to each of those creatures. You create a Mutagen token for each creature dealt damage this way. (They're artifacts with "1, T, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")