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.

Breathkeeper Seraph

Flying, soulbond (You may pair this creature with another unpaired creature when either enters. They remain paired for as long as you control both of them.)
As long as Breathkeeper Seraph is paired with another creature, each of those creatures has "When this creature dies, you may return it to the battlefield under its owner's control at the beginning of your next upkeep."

Adarkar Valkyrie

Flying, vigilance
{T}: When target creature other than this creature dies this turn, return that card to the battlefield under your control.

Ao, the Dawn Sky

Flying, vigilance
When Ao dies, choose one —
• Look at the top seven cards of your library. Put any number of nonland permanent cards with total mana value 4 or less from among them onto the battlefield. Put the rest on the bottom of your library in a random order.
• Put two +1/+1 counters on each permanent you control that's a creature or Vehicle.

Fanatical Devotion

Sacrifice a creature: Regenerate target creature.

Angelic Renewal

Whenever a creature is put into your graveyard from the battlefield, you may sacrifice this enchantment. If you do, return that card to the battlefield.

Wayward Angel

Flying, vigilance
Threshold — As long as there are seven or more cards in your graveyard, this creature gets +3/+3, is black, has trample, and has "At the beginning of your upkeep, sacrifice a creature."

Angelic Purge

As an additional cost to cast this spell, sacrifice a permanent.
Exile target artifact, creature, or enchantment.