Witch Engine is a rare Creature — Horror card from Urza's Saga (USG), collector number 169. Current market price: $0.49, TCGplayer market prices via Scryfall.
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.) {T}: Add {B}{B}{B}{B}. Target opponent gains control of this creature. (Activate only as an instant.)