Requires

Fury Storm must be in hand. Sedgemoor Witch must be on the battlefield. You have cast your commander from your command zone this game. An additional instant or sorcery in hand with the mana to cast it, or an opponent has cast an as of yet unresolved instant or sorcery spell. Mana needed:

Steps

1. Cast your additional instant or sorcery spell, or wait for an opponent to cast one.
2. Sedgemoor Witch triggers, creating a Pest creature token.
3. Cast Fury Storm targeting the instant or sorcery spell.
4. Sedgemoor Witch triggers, creating a Pest creature token.
5. Fury Storm triggers, copying itself for each time you have cast your commander from your command zone this game and choosing the original copy of Fury Storm as the target.
6. Sedgemoor Witch triggers for each copy, creating a Pest creature token each time.
7. Resolve a Fury Storm copy, copying Fury Storm and choosing the original Fury Storm as the target.
8. Sedgemoor Witch triggers, creating a Pest creature token.
9. Repeat from step 7.

Results