One with the Multiverse

While casting a card with the prototype ability using the last ability of One with the Multiverse, you can either choose to cast it normally or choose to cast it as a prototyped spell. In either case, you won't pay its mana cost.

While casting a spell without paying its mana cost using the last ability, you can't pay alternative costs, but you may choose to pay any optional additional costs the spell may have (such as a kicker cost). You still must pay any mandatory additional costs.

If One with the Multiverse leaves the battlefield and later returns to the battlefield (or you play a second one), it's considered a new object and you may cast a spell using its last ability regardless of whether or not you did so earlier this turn using the enchantment that was on the battlefield before.