Kulrath Knight

Flying
Wither (This deals damage to creatures in the form of -1/-1 counters.)
Creatures your opponents control with counters on them can't attack or block.

Novice Dissector

{1}, Sacrifice another creature: Put a +1/+1 counter on target creature. Activate only as a sorcery.

Myr Scrapling

Sacrifice Myr Scrapling: Put a +1/+1 counter on target creature.

Festering Mummy

When Festering Mummy dies, you may put a -1/-1 counter on target creature.

Fume Spitter

Sacrifice Fume Spitter: Put a -1/-1 counter on target creature.

Iron Bully

Menace (This creature can't be blocked except by two or more creatures.)
When Iron Bully enters, put a +1/+1 counter on target creature.

Greater Werewolf

At end of combat, put a -0/-2 counter on each creature blocking or blocked by Greater Werewolf.

Oubliette

When Oubliette enters, target creature phases out until Oubliette leaves the battlefield. Tap that creature as it phases in this way. (Auras and Equipment phase out with it. While permanents are phased out, they're treated as though they don't exist.)

Pith Driller

({B/P} can be paid with either {B} or 2 life.)
When Pith Driller enters, put a -1/-1 counter on target creature.