Geometer's Arthropod is a rare Creature — Fractal Crab card from Secrets of Strixhaven (SOS), collector number 191. Current market price: $0.32 (foil $0.34), TCGplayer market prices via Scryfall.
Whenever you cast a spell with {X} in its mana cost, look at the top X cards of your library. Put one of them into your hand and the rest on the bottom of your library in a random order.