Coral Fighters is a uncommon Creature — Merfolk Soldier card from Duel Decks: Venser vs. Koth (DDI), collector number 4. Current market price: $0.16, TCGplayer market prices via Scryfall.
Whenever this creature attacks and isn't blocked, look at the top card of defending player's library. You may put that card on the bottom of that player's library.