Guile + Flusterstorm

Prerequisites

You have an additional instant or sorcery card in hand.

Steps

1. Cast the additional instant or sorcery spell.
2. Holding priority, cast Flusterstorm by paying {U}, targeting the instant or sorcery.
3. Flusterstorm's storm ability triggers, creating a copy of Flusterstorm for each spell you've cast before it this turn, with each copy targeting the original Flusterstorm.
4. Resolve a copy of Flusterstorm, exiling Flusterstorm and allowing you to cast it from exile without paying its mana cost, targeting the instant or sorcery spell.
5. Repeat from step 3.