Tributary Vaulter

Most tribal pump creatures ask you to attack, chaining the reward to combat and to the risk of committing bodies to a swing. This one keys off tapping instead, and any tap will do: crewing a vehicle, paying an activated cost, convoking a spell, or turning sideways in combat. Each time it taps, another Merfolk you control gets +2/+0 until end of turn, so a 1/3 flyer becomes a repeatable engine as long as you have a reason to tap it and a second fish to point the buff at. The flying is doing quiet work here: an evasive body survives the trigger and swings over most blockers while the ground Merfolk absorb the boost. Two constraints hold the design in check. The 1/3 body threatens little on its own, and the buff only ever adds power, never toughness, so it accelerates a race rather than breaking a stalemate open. It is a support piece built to make a wide Merfolk board hit harder, and its ceiling is set entirely by how many ways a deck finds to tap it outside of combat.