Necromancer's Haven

Necromancer's Haven enters the battlefield tapped.
{t}: add {b} or {u} to your mana pool.
{t}: add {b}{u} to your mana pool. Use this mana only to cast Zombie creature spells.
{1}{b}{t}: all zombies you control gain +1/+1 and menace until end of turn.
{x}{x}{t}: put X 2/4 black Zombie Knight creature tokens onto the battlefield.
Brains