Spitter Xeno

Acid Blood 3
{t}{x}: Deal X damage to target creature or planeswalker, then add X Acid counters to whatever received the damage
Acid counters deal X damage each upkeep to permanent it's attached to, where X is how many turns the permanent has had the counter on
Remove an Acid counter by tapping the permanent and paying X life, where X is how many turns the permanent has had the
counter on