Rottenmouth Viper is a mythic Creature — Elemental Snake card from Bloomburrow Promos (PBLB), collector number 107s. Current market price: — (foil $9.87), TCGplayer market prices via Scryfall.
As an additional cost to cast this spell, you may sacrifice any number of nonland permanents. This spell costs {1} less to cast for each permanent sacrificed this way. Whenever this creature enters or attacks, put a blight counter on it. Then for each blight counter on it, each opponent loses 4 life unless that player sacrifices a nonland permanent of their choice or discards a card.