Cayth, Famed Mechanist, Mana Echoes, and Corridor Monitor

Prerequisites

• Cayth, Famed Mechanist on the battlefield
• Mana Echoes on the battlefield
• Corridor Monitor on the battlefield
• available

Steps

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

Results

• Infinite ETB
• Infinite colorless mana
• Infinite creature tokens