Nemesis Trap is a uncommon Instant — Trap card from Commander 2011 (CMD), collector number 91. Current market price: $0.14, TCGplayer market prices via Scryfall.
If a white creature is attacking, you may pay {B}{B} rather than pay this spell's mana cost. Exile target attacking creature. Create a token that's a copy of that creature. Exile it at the beginning of the next end step.