Cateran Slaver is a rare Creature — Horror Mercenary card from Mercadian Masques (MMQ), collector number 125. Current market price: $0.72 (foil $21.71), TCGplayer market prices via Scryfall.
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.) {5}, {T}: Search your library for a Mercenary permanent card with mana value 5 or less, put it onto the battlefield, then shuffle.