Champions of the Shoal

Behold as an additional cost gives this its whole shape: you exile a Merfolk you control or from your hand to cast, and while the 4/6 lives, that card sits hostage in exile until the creature leaves. That framing turns what would otherwise be a plain tempo body into a two-part transaction. The exiled Merfolk is a deposit, not a discard; you get it back the moment the board changes, which quietly hedges the card advantage the additional cost would normally bleed. Where it earns its keep is the tap-and-stun engine. The trigger fires when it enters and when it becomes tapped, and a stun counter forces the tapped creature to spend its next untap step clearing the counter before it can act again. The relevant loop, then, is effects that keep tapping the Champions after it has already resolved: any untap engine, any way to tap it for value, re-arms the disruption and sends another opposing creature to the sideline for an extra turn. Note that vigilance does not help here, because a vigilant attacker never becomes tapped and so never fires the ability; the trigger wants the creature tapping, not staying up. The 6 toughness is doing deliberate work, surviving the combat and burn a tapper this disruptive invites. The design tension is the additional cost itself: you cannot cast it without another Merfolk to feed it, so it demands a board already leaning tribal and rewards that commitment with a control piece that keeps one threat perpetually a step behind.