Champions of the Shoal (ECL 46)

Creature — Merfolk Soldier • Mana cost: {3}{U} • Lorwyn Eclipsed • Rare

As an additional cost to cast this spell, behold a Merfolk and exile it. (Exile a Merfolk you control or a Merfolk card from your hand.)
Whenever this creature enters or becomes tapped, tap up to one target creature and put a stun counter on it.
When this creature leaves the battlefield, return the exiled card to its owner's hand.

Illustrated by Daniel Zrom.