Slith Bloodletter

Whenever Slith Bloodletter deals combat damage to a player, put a +1/+1 counter on it.
{1}{B}: Regenerate Slith Bloodletter.

Bloodforged Battle-Axe

Equipped creature gets +2/+0.
Whenever equipped creature deals combat damage to a player, create a token that's a copy of Bloodforged Battle-Axe.
Equip {2}

Felix Five-Boots

Menace, ward {2}
If a creature you control dealing combat damage to a player causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

The Peregrine Dynamo

Haste
{1}, {T}: Copy target activated or triggered ability you control from another legendary source that's not a commander. You may choose new targets for the copy. (Mana abilities can't be targeted.)

Slitherbore Pathway

Darkbore Pathway

Darkbore Pathway // Slitherbore Pathway

Arcbound Slith

Whenever Arcbound Slith deals combat damage to a player, put a +1/+1 counter on it.
Modular 1 (This creature enters the battlefield with a +1/+1 counter on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Slith Strider

Whenever Slith Strider becomes blocked, draw a card.
Whenever Slith Strider deals combat damage to a player, put a +1/+1 counter on it.

Slith Predator

Trample
Whenever Slith Predator deals combat damage to a player, put a +1/+1 counter on it.