Cathar's Companion is a common Creature — Dog card from Shadows over Innistrad (SOI), collector number 9. Current market price: $0.16 (foil $0.18), TCGplayer market prices via Scryfall.
Whenever you cast a noncreature spell, this creature gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)