Cayth, Famed Mechanist, Mana Echoes, and Sparring Mummy

Prerequisites

• Cayth, Famed Mechanist on the battlefield
• Mana Echoes on the battlefield
• Sparring Mummy on the battlefield
• available

Steps

1. Activate Cayth by paying and tapping it, creating a copy of the Sparring Mummy token
2. When the Sparring Mummy token enters the battlefield, it and Mana Echoes trigger
3. Resolve the Sparring Mummy trigger, untapping Cayth Resolve the Mana Echoes trigger, adding for each creature you control that shares a type with the Sparring Mummy token
4. Repeat

Results

• Infinite ETB
• Infinite colorless mana
• Infinite creature tokens