Menace Creatures you control have wither. (They deal damage to creatures in the form of -1/-1 counters.) Whenever a creature an opponent controls dies, if its toughness was less than 1, draw a card.

Whenever this creature enters or attacks, put a -1/-1 counter on up to one target creature. Creatures your opponents control with -1/-1 counters on them can't block.

Flying, deathtouch Whenever an opponent loses life, you gain that much life. (Damage causes loss of life.)

Whenever this creature or another creature you control dies, each opponent loses 1 life and you gain 1 life.

Protection from Humans Pay 1 life, Sacrifice another creature: Put a -1/-1 counter on up to one target creature and draw a card. {B}{B}, Discard a card: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

When this artifact enters, put a -1/-1 counter on target creature. {4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.) Whenever you tap a Swamp for mana, add an additional {B}.

Wither (This deals damage to creatures in the form of -1/-1 counters.) Whenever a creature an opponent controls with a -1/-1 counter on it dies, you may return that card to the battlefield under your control.

When The Meathook Massacre enters, each creature gets -X/-X until end of turn. Whenever a creature you control dies, each opponent loses 1 life. Whenever a creature an opponent controls dies, you gain 1 life.

Haste Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni. Sacrifice another creature: Yahenni gains indestructible until end of turn.

Whenever you put one or more -1/-1 counters on a creature, create that many 1/1 black Insect creature tokens.

Search your library for a card, then shuffle and put that card on top. You lose 2 life.