Yarok, the Desecrated + Prototype Portal + Corridor Monitor + Gilded Lotus

Yarok, the Desecrated

Prototype Portal

Corridor Monitor

Gilded Lotus

How it works

1. Activate Gilded Lotus by tapping it, adding three mana of any color.
2. Activate Prototype Portal by paying 2 and tapping it, creating a token copy of Corridor Monitor.
3. The Corridor Monitor token enters the battlefield, untapping Prototype Portal and Gilded Lotus.
4. Repeat.