Prismari, the Inspiration, and Fork

Prerequisites

• Prismari, the Inspiration on the battlefield
• Fork in hand
• available

Steps

1. Cast any other instant or sorcery by paying its mana cost
2. Holding priority, cast Fork by paying its mana cost, targeting the instant or sorcery cast in step 1
3. Fork's storm ability triggers, creating at least one copy of Fork targeting the original Fork
4. Resolve a copy of Fork, copying Fork targeting the original Fork
5. Repeat step 4

Results

• Infinite magecraft triggers