Marelle, the Gravewarden

Whenever another creature dies, put a
Gravestone counter on Marelle, the Gravewarden.
Gravestone counters remain on Marelle, the
Gravewarden as it moves to any zone other than
a player's hand or library.
{2}, {t}, Remove X Gravestone counters from
Marelle, the Gravewarden: Return target creature
card with converted mana cost X from your
graveyard to the battlefield.