Improvisation Capstone [Secrets of Strixhaven]

Exile cards from the top of your library until you exile cards with total mana value 4 or greater. You may cast any number of spells from among them without paying their mana costs.
Paradigm (Then exile this spell. After you first resolve a spell with this name, you may cast a copy of it from exile without paying its mana cost at the beginning of each of your first main phases.)