Thundertrap Trainer is a common Token Creature — Otter Wizard card from Bloomburrow Tokens (TBLB), collector number 9. Current market price: $0.43, TCGplayer market prices via Scryfall.
When this creature enters, look at the top four cards of your library. You may reveal a noncreature, nonland card from among them and put it into your hand. Put the rest on the bottom of your library in a random order. (This token's mana cost is {1}{U}.)