Aberrant Manawurm (Secrets of Strixhaven #138)

Creature — Wurm - {3}{G}
Trample
Whenever you cast an instant or sorcery spell, this creature gets +X/+0 until end of turn, where X is the amount of mana spent to cast that spell.
2/5
„"What is the equation for terror?"
—Lost research note, Paradox Gardens“