Soul Foundry + Corridor Monitor + Gilded Lotus + Panharmonicon

Soul Foundry

Corridor Monitor

Gilded Lotus

Panharmonicon

How it works

1. Activate Gilded Lotus by tapping it, adding three mana of any color.
2. Activate Soul Foundry by paying 2 and tapping it, creating a token copy of Corridor Monitor.
3. When the Corridor Monitor token enters the battlefield, it triggers twice, untapping Soul Foundry and Gilded Lotus.
4. Repeat.

This loop transforms Soul Foundry into an engine for infinite replication by using Corridor Monitor as the cloned creature, whose entry triggers are doubled by Panharmonicon to untap both the Foundry and Gilded Lotus. Because Gilded Lotus produces three mana when tapped and the Foundry only costs two to activate, this entire sequence is mana-positive, allowing you to generate infinite colored mana, infinite tokens, and an endlessly repeating cycle of enters-the-battlefield triggers.