Mutating Contagion

Mutating Contagion is all creature types in addition to its own.
When Mutating Contagion enters the battlefield, choose a creature type. At the beginning of each upkeep, put a +1/+1 counter
on Mutating Contagion for each creature on the battlefield of the chosen type.
{b}, Remove a +1/+1 counter from Mutating Contagion: It deals 1 damage to target creature or player.