Ornery Kudu

When Ornery Kudu enters, put a -1/-1 counter on target creature you control.

Decimator Beetle

When Decimator Beetle enters, put a -1/-1 counter on target creature you control.
Whenever Decimator Beetle attacks, remove a -1/-1 counter from target creature you control and put a -1/-1 counter on up to one target creature defending player controls.

Hapatra, Vizier of Poisons

Whenever Hapatra, Vizier of Poisons deals combat damage to a player, you may put a -1/-1 counter on target creature.
Whenever you put one or more -1/-1 counters on a creature, create a 1/1 green Snake creature token with deathtouch.

Soulstinger

When Soulstinger enters, put two -1/-1 counters on target creature you control.
When Soulstinger dies, you may put a -1/-1 counter on target creature for each -1/-1 counter on Soulstinger.

Supernatural Stamina

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Oashra Cultivator

{2}{G}, {T}, Sacrifice Oashra Cultivator: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Baleful Ammit

Lifelink
When Baleful Ammit enters, put a -1/-1 counter on target creature you control.

Defiant Greatmaw

When Defiant Greatmaw enters, put two -1/-1 counters on target creature you control.
Whenever you put one or more -1/-1 counters on Defiant Greatmaw, remove a -1/-1 counter from another target creature you control.