Cayth, Famed Mechanist + Mana Echoes + Corridor Monitor

Cayth, Famed Mechanist

Mana Echoes

Corridor Monitor

How it works

1. Activate Cayth by paying 2 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
4. Resolve the Mana Echoes trigger, adding C for each creature you control that shares a type with the Corridor Monitor token.
5. Repeat.