Cinderbones

Wither (This deals damage to creatures in the form of -1/-1 counters.)
{1}{B}: Regenerate this creature.

Corrosive Mentor

Black creatures you control have wither. (They deal damage to creatures in the form of -1/-1 counters.)

Needle Specter

Flying
Wither (This deals damage to creatures in the form of -1/-1 counters.)
Whenever this creature deals combat damage to a player, that player discards that many cards.

Lockjaw Snapper

Wither (This deals damage to creatures in the form of -1/-1 counters.)
When this creature dies, put a -1/-1 counter on each creature with a -1/-1 counter on it.

Necroskitter

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.

Fang Skulkin

{2}: Target black creature gains wither until end of turn. (It deals damage to creatures in the form of -1/-1 counters.)

Sickle Ripper

Wither (This deals damage to creatures in the form of -1/-1 counters.)

Massacre Girl, Known Killer

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.

Thornwatch Scarecrow

This creature has wither as long as you control a green creature. (It deals damage to creatures in the form of -1/-1 counters.)
This creature has vigilance as long as you control a white creature.

Smoldering Butcher

Midnight Banshee

Wither (This deals damage to creatures in the form of -1/-1 counters.)
At the beginning of your upkeep, put a -1/-1 counter on each nonblack creature.

Blazethorn Scarecrow

This creature has haste as long as you control a red creature.
This creature has wither as long as you control a green creature. (It deals damage to creatures in the form of -1/-1 counters.)

Blight Sickle

Equipped creature gets +1/+0 and has wither. (It deals damage to creatures in the form of -1/-1 counters.)
Equip {2}