Worthy Cause

Buyback {2} (You may pay an additional {2} as you cast this spell. If you do, put this card into your hand as it resolves.)
As an additional cost to cast this spell, sacrifice a creature.
You gain life equal to the sacrificed creature's toughness.

Riptide Shapeshifter

{2}{U}{U}, Sacrifice Riptide Shapeshifter: Choose a creature type. Reveal cards from the top of your library until you reveal a creature card of that type. Put that card onto the battlefield and shuffle the rest into your library.

Seeker of Skybreak

Whiteout

All creatures lose flying until end of turn.
Sacrifice a snow land: Return Whiteout from your graveyard to your hand.