Cayth, Famed Mechanist, Mana Echoes, and Umbral Mantle

Prerequisites

• Cayth, Famed Mechanist on the battlefield
• Mana Echoes on the battlefield
• Umbral Mantle on the battlefield
• You control at least one creature token
• You control at least four creatures that share a creature type with the creature token
• Cayth does not have summoning sickness
• available

Steps

1. Activate Cayth by paying and tapping it, creating a token copy of a creature token you control
2. When the creature token enters the battlefield, Mana Echoes triggers, adding for each creature you control that shares a creature type with it
3. Activate Cayth by paying and untapping it, giving it +2/+2 until end of turn
4. Repeat

Results

• Infinite ETB
• Infinite colorless mana
• Infinite proliferate
• Infinite copies of creature tokens you control
• Infinitely large Cayth until end of turn