Requires

Thousand-Year Storm must be on the battlefield. Spelljack must be in hand. You have an additional instant card in hand. Mana needed: plus enough mana to cast the additional instant card

Steps

1. Cast any other instant card from your hand by paying its mana cost.
2. Holding priority, cast Spelljack by paying targeting the instant.
3. Thousand-Year Storm triggers, creating at least one copy of Spelljack that is targeting the original Spelljack.
4. Resolve the first copy of Spelljack, countering the original Spelljack and exiling it with the ability to cast it for free from exile.
5. All remaining copies of Spelljack fail to resolve due to having no legal targets.
6. Cast Spelljack from exile without paying its mana cost, targeting the instant cast in Step 1.
7. Repeat from step 3.

Results