Narset's Reversal + Twincast

Prerequisites

You have an additional instant or sorcery card in hand with valid targets as applicable.

Steps

1. Cast any instant or sorcery by paying its mana cost.
2. Holding priority, cast Twincast by paying its mana cost, targeting the instant or sorcery cast in step 1.
3. Cast Narset's Reversal by paying {U}{U}, copying Twincast targeting the spell cast in step 1 and returning the original Twincast to your hand.
4. Cast Twincast by paying its mana cost, copying the copy of Twincast, targeting the copy of Twincast.
5. Resolve the copy of Twincast, creating a copy of Twincast targeting the copy of Twincast.
6. Repeat step 5.