Emberheart Challenger is a rare Creature — Mouse Warrior card from Secret Lair Promo (SLP), collector number 48. Current market price: $14.02 (foil $199.99), TCGplayer market prices via Scryfall.
Haste Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.) Valiant — Whenever this creature becomes the target of a spell or ability you control for the first time each turn, exile the top card of your library. Until end of turn, you may play that card.