Requires

Rootha, Mercurial Artist must be on the battlefield. Expansion // Explosion must be in hand. Mana needed:

Steps

1. Cast an instant or sorcery spell, or wait for an opponent to cast one.
2. Holding priority, cast Expansion by paying , targeting the spell.
3. Activate Rootha by paying and returning it to your hand, copying Expansion, with the copy targeting the original Expansion.
4. Resolve the copy of Expansion, copying Expansion, targeting the original Expansion.
5. Repeat step 4.

Results