Adaptive Training Post + Expansion // Explosion

Prerequisites

You have an instant or sorcery card in hand with mana value 4 or less.

Steps

1. Cast the additional instant or sorcery by paying its mana cost.
2. If Adaptive Training Post had two charge counters on it, it triggers, putting a charge counter on it.
3. Holding priority, activate Adaptive Training Post by removing three charge counters from it, copying the next instant or sorcery spell you cast this turn.
4. Cast Expansion by paying its mana cost, targeting the spell cast in step 1.
5. Adaptive Training Post triggers, copying Expansion, with the copy targeting the original Expansion.
6. Resolve the copy of Expansion, copying the original Expansion, with the copy targeting the original Expansion.
7. Repeat step 5.