Rootha, Mastering the Moment (Borderless)

At the beginning of combat on your turn, if you've cast an instant or sorcery spell this turn, create an X/X blue and red Elemental creature token with flying and haste, where X is the greatest mana value among instant and sorcery spells you've cast this turn.

"The great thrill of perfection is that we'll always be chasing it."