Greater Good

Sacrifice a creature: Draw cards equal to the sacrificed creature's power, then discard three cards.

Buried Alive

Search your library for up to three creature cards, put them into your graveyard, then shuffle.

Death's Oasis

Whenever a nontoken creature you control dies, mill two cards. Then return a creature card with lesser mana value than the creature that died from your graveyard to your hand.
{1}, Sacrifice Death's Oasis: You gain life equal to the highest mana value among creatures you control.

Spore Frog

Sacrifice Spore Frog: Prevent all combat damage that would be dealt this turn.

Nethroi, Apex of Death

Mutate {4}{G/W}{B}{B} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Deathtouch, lifelink
Whenever this creature mutates, return any number of target creature cards with total power 10 or less from your graveyard to the battlefield.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Caustic Caterpillar

{1}{G}, Sacrifice Caustic Caterpillar: Destroy target artifact or enchantment.