Narset's Reversal + Return the Favor

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 Return the Favor by paying {R}{R} plus an additional {1} to choose its first mode, targeting the instant or sorcery cast in step 1.
3. Cast Narset's Reversal by paying {U}{U}, copying Return the Favor targeting the spell cast in step 1 and returning the original Return the Favor to your hand.
4. Cast Return the Favor by paying its mana cost, copying the copy of Return the Favor, targeting the copy of Return the Favor.
5. Resolve the copy of Return the Favor, creating a copy of Return the Favor targeting the copy of Return the Favor.
6. Repeat step 5.