Stronghold Overseer is a rare Creature — Demon card from Time Spiral (TSP), collector number 133. Current market price: $0.52 (foil $4.57), TCGplayer market prices via Scryfall.
Flying Shadow (This creature can block or be blocked by only creatures with shadow.) {B}{B}: Creatures with shadow get +1/+0 until end of turn and creatures without shadow get -1/-0 until end of turn.