Requires

Mythos of Illuna must be in hand. Radiate must be in hand. Eternal Witness must be on the battlefield. There are permanents on the battlefield that enter the battlefield untapped and produce at least . Mana needed:

Steps

1. Cast Mythos of Illuna targeting anything but Eternal Witness, holding priority, and then cast Radiate targeting Mythos of Illuna.
2. When Radiate resolves you will have Mythos copies targeting every targetable permanent (except what the original Mythos card is targeting).
3. When each of the copies resolve, target Radiate in your graveyard with the new Eternal Witness token's ability and return Radiate to your hand.
4. Before the original Mythos of Illuna card resolves, cast Radiate again targeting Mythos by spending mana from the tokens you just created.
5. Repeat this process, effectively doubling the number of copies created, allowing you to return Radiate and another card with two Witness triggers.
6. Repeat.

Results