Abyssal Gorestalker

When Abyssal Gorestalker enters the battlefield, each player sacrifices two creatures.

Aggravated Assault

{3}{R}{R}: Untap all creatures you control. After this main phase, there is an additional combat phase followed by an additional main phase. Activate only as a sorcery.

Access Denied

Counter target spell. Create X 1/1 colorless Thopter artifact creature tokens with flying, where X is that spell's mana value.

Agent of the Shadow Thieves

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, put a +1/+1 counter on this creature. It gains deathtouch and indestructible until end of turn."

Altar's Reap

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Acererak the Archlich

When Acererak the Archlich enters the battlefield, if you haven't completed Tomb of Annihilation, return Acererak the Archlich to its owner's hand and venture into the dungeon.
Whenever Acererak the Archlich attacks, for each opponent, you create a 2/2 black Zombie creature token unless that player sacrifices a creature.

Ahn-Crop Invader

As long as it's your turn, Ahn-Crop Invader has first strike.
{1}, Sacrifice another creature: Ahn-Crop Invader gets +2/+0 until end of turn.

Thraximundar

Haste
Whenever Thraximundar attacks, defending player sacrifices a creature.
Whenever a player sacrifices a creature, you may put a +1/+1 counter on Thraximundar.

Abyssal Persecutor

Flying, trample
You can't win the game and your opponents can't lose the game.

Accursed Horde

{1}{B}: Target attacking Zombie gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it. If its toughness is 0 or less, it's still put into its owner's graveyard.)