Deekah, Fractal Theorist is a rare Legendary Creature — Human Wizard card from Commander 2021 (C21), collector number 353. Current market price: $4.21, TCGplayer market prices via Scryfall.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is that spell's mana value. {3}{U}: Target creature token can't be blocked this turn.