Sliver creatures you control have "Whenever this creature deals combat damage to a player, put a +1/+1 counter on it."

Myriad, myriad (Whenever this creature attacks, for each opponent other than defending player, you may create a token that's a copy of this creature that's tapped and attacking that player or a planeswalker they control. Then do it again. Exile the tokens at end of combat.)

Whenever this creature deals combat damage to a player, put a +1/+1 counter on target creature you control.

Whenever this creature deals combat damage to a player, you get (two energy counters).

Pay : Put a +1/+1 counter on this creature.

Ninjutsu

This creature enters with a deathtouch counter on it.

Whenever this creature deals combat damage to a player, you may remove a deathtouch counter from it. When you do, exile target artifact or enchantment that player controls.

Trample

Whenever this creature deals combat damage to a player, put a +1/+1 counter on it.

Whenever this creature deals combat damage to a creature, tap that creature and it doesn't untap during its controller's next untap step.

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Whenever a creature you control with deathtouch deals combat damage to a player, that player gets two poison counters. (A player with ten or more poison counters loses the game.)

Whenever this creature deals combat damage to a player, untap target creature or land.

: This creature deals 1 damage to target creature with flying.

Whenever this creature deals damage to a creature, tap that creature and it doesn't untap during its controller's next untap step.

Flying

Whenever this creature deals combat damage to a player, you may destroy target artifact that player controls.

Legendary Snakes you control have shroud. (They can't be the targets of spells or abilities.)

Whenever this creature deals combat damage to a creature, tap that creature and it doesn't untap during its controller's next untap step.

: Target creature blocks this creature this turn if able.

Whenever this creature deals combat damage to a creature, tap that creature and it doesn't untap during its controller's next untap step.

Whenever a creature you control deals combat damage to a player, put a +1/+1 counter on that creature.

Unlock Ability — Creatures you control with +1/+1 counters on them have reach and trample.

Whenever this creature deals combat damage to a creature, destroy that creature at end of combat.

Whenever this creature deals combat damage to a player, you may draw a card.

Prowler can't be blocked by creatures with power 2 or less.

Whenever Prowler deals combat damage to a player, put a +1/+1 counter on another target creature you control.

Equipped creature has trample and "Whenever this creature deals combat damage to a player, put that many +1/+1 counters on it."

Equip

Reach

Whenever you cast a spell that targets Legolas, put a +1/+1 counter on Legolas.

Whenever you cast a spell that targets a creature you don't control, Legolas deals damage equal to its power to up to one target creature.

When this creature enters, put a +1/+1 counter on target creature you control.