Seafloor Stalker is a common Creature — Merfolk Rogue card from Zendikar Rising (ZNR), collector number 78. Current market price: $0.18 (foil $0.06), TCGplayer market prices via Scryfall.
{4}{U}: This creature gets +1/+0 until end of turn and can't be blocked this turn. This ability costs {1} less to activate for each creature in your party. (Your party consists of up to one each of Cleric, Rogue, Warrior, and Wizard.)