At the beginning of each player's upkeep, that player sacrifices a non-Zombie creature. At the beginning of the end step, if no creatures are on the battlefield, sacrifice Call to the Grave.
Flash When Caller of the Claw enters the battlefield, create a 2/2 green Bear creature token for each nontoken creature put into your graveyard from the battlefield this turn.
Flying When Celestial Gatekeeper dies, exile it, then return up to two target Bird and/or Cleric permanent cards from your graveyard to the battlefield.
{T}: Add {G}. Centaur Garden deals 1 damage to you. Threshold — {G}, {T}, Sacrifice Centaur Garden: Target creature gets +3/+3 until end of turn. Activate only if seven or more cards are in your graveyard.