Manifold Mouse is a rare Creature — Mouse Soldier card from Secret Lair Promo (SLP), collector number 47. Current market price: $0.44 (foil $4.00), TCGplayer market prices via Scryfall.
Offspring {2} (You may pay an additional {2} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.) At the beginning of combat on your turn, target Mouse you control gains your choice of double strike or trample until end of turn.