Prototype Portal + Corridor Monitor + Gilded Lotus + Doubling Season

Prototype Portal

Corridor Monitor

Gilded Lotus

Doubling Season

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 two token copies of Corridor Monitor.
3. The Corridor Monitor tokens enter the battlefield, untapping Prototype Portal and Gilded Lotus.
4. Repeat.