Deathmask Nezumi is a common Creature — Rat Shaman card from Saviors of Kamigawa (SOK), collector number 66. Current market price: $0.17 (foil $0.39), TCGplayer market prices via Scryfall.
As long as you have seven or more cards in hand, this creature gets +2/+1 and has fear. (It can't be blocked except by artifact creatures and/or black creatures.)