Frelsari, Tribute to the Dead

Whenever a sphinx dies, you get an
experience counter.
{u}{u} {t}, Exile Frelsari, Tribute to the Dead:
return half of X, rounded down, creatures with
converted mana cost X or less from your
graveyard to the battlefield, where X is the
amount of experience counters you have.
This ability costs {1} more to activate for each
experience counter you have.