Cayth, Famed Mechanist, Mana Echoes, and Breaching Hippocamp

Prerequisites

• Cayth, Famed Mechanist on the battlefield
• Mana Echoes on the battlefield
• Breaching Hippocamp on the battlefield
• available

Steps

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

Results

• Infinite ETB
• Infinite colorless mana
• Infinite creature tokens