Mairum, Gaia's Caretaker

Mairum, Gaia's Caretaker enters the battlefield
with one +1/+1 counter on it.
Cards with converted mana value X in your
graveyard have Dredge 2, where X is the number
of +1/+1 counters on Mairum, Gaia's Caretaker.
{g},{t}: Add or remove a +1/+1 counter from
Mairum, Gaia's Caretaker.