Sacrifice

As an additional cost to cast this spell, sacrifice a creature.
Add an amount of {B} equal to the sacrificed creature's mana value.

Deathrite Shaman

{T}: Exile target land card from a graveyard. Add one mana of any color.
{B}, {T}: Exile target instant or sorcery card from a graveyard. Each opponent loses 2 life.
{G}, {T}: Exile target creature card from a graveyard. You gain 2 life.

Dark Ritual

Spoils of Evil

For each artifact or creature card in target opponent's graveyard, add {C} and you gain 1 life.

Songs of the Damned

Add {B} for each creature card in your graveyard.

Mask of Avacyn

Equipped creature gets +1/+2 and has hexproof. (It can't be the target of spells or abilities your opponents control.)
Equip {3}

Metamorphosis

As an additional cost to cast this spell, sacrifice a creature.
Add X mana of any one color, where X is 1 plus the sacrificed creature's mana value. Spend this mana only to cast creature spells.

Jenova, Ancient Calamity

At the beginning of combat on your turn, put a number of +1/+1 counters equal to Jenova's power on up to one other target creature. That creature becomes a Mutant in addition to its other types.
Whenever a Mutant you control dies during your turn, you draw cards equal to its power.

Bloodline Pretender

Changeling (This card is every creature type.)
As this creature enters, choose a creature type.
Whenever another creature you control of the chosen type enters, put a +1/+1 counter on this creature.

Soldevi Adnate

{T}, Sacrifice a black or artifact creature: Add an amount of {B} equal to the sacrificed creature's mana value.

The Gitrog, Ravenous Ride

Trample, haste
Whenever The Gitrog deals combat damage to a player, you may sacrifice a creature that saddled it this turn. If you do, draw X cards, then put up to X land cards from your hand onto the battlefield tapped, where X is the sacrificed creature's power.
Saddle 1

Viscera Seer

Sacrifice a creature: Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Yargle and Multani

Masked Vandal

Changeling (This card is every creature type.)
When this creature enters, you may exile a creature card from your graveyard. If you do, exile target artifact or enchantment an opponent controls.

Yargle, Glutton of Urborg

Changeling Outcast

Changeling (This card is every creature type.)
This creature can't block and can't be blocked.

Warren Soultrader

Pay 1 life, Sacrifice another creature: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Bygone Colossus

Warp {3} (You may cast this card from your hand for its warp cost. Exile this creature at the beginning of the next end step, then you may cast it from exile on a later turn.)

Rise of the Dark Realms

Put all creature cards from all graveyards onto the battlefield under your control.

Carrion Feeder

This creature can't block.
Sacrifice a creature: Put a +1/+1 counter on this creature.

Realmwalker

Changeling (This card is every creature type.)
As this creature enters, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.

Ghalta, Primal Hunger

This spell costs {X} less to cast, where X is the total power of creatures you control.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)