Form of the Mulldrifter

If Form of the Mulldrifter leaves the battlefield, any Mulldrifters on the stack or battlefield remain Mulldrifters.

Mulldrifter is a 2/2 blue Elemental creature with mana cost {4}{U} and the abilities flying, “When Mulldrifter enters the battlefield, draw two cards,” and evoke {2}{U}.

Evoke {2}{U} means “You may cast this spell by paying {2}{U} rather than its mana cost.” and “When this permanent enters the battlefield, if its evoke cost was paid, its controller sacrifices it.”