Sarpoza, the First Warlock

Sarpoza, the First Warlock enters the battlefield
with a +1/+1 counter on it for each color of
mana spent to cast it.
Whenever you cast your first multicolored
instant or sorcery each turn, put a +1/+1 counter
on Sarpoza for each color of mana spent to cast
that spell.
This creature cannot be damaged, destroyed, or
exiled by spells you control.