Geometric Nexus is a rare Artifact card from Commander 2021 (C21), collector number 77. Current market price: $0.36, TCGplayer market prices via Scryfall.
Whenever a player casts an instant or sorcery spell, put a number of charge counters on this artifact equal to that spell's mana value. {6}, {T}, Remove all charge counters from this artifact: Create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is the number of charge counters removed this way.