Omnath, Locus of Power

{t}, Sacrifice a land: Return target nonland
permanent an opponent controls to its owners
hand if its converted mana cost is less than or
equal to the number of elementals you control.
Whenever you cast an elemental spell, you may discard a card. If you do, return target land card
from your graveyardto your hand. If you control
5 or more elementals, return it to the battlefield instead.