Gilded Lotus + Umbral Mantle + Xenic Poltergeist

Gilded Lotus

Umbral Mantle

Xenic Poltergeist

How it works

1. Activate Xenic Poltergeist by tapping it, targeting Gilded Lotus.
2. Activate Umbral Mantle's equip ability by paying 0, attaching it to the Gilded Lotus.
3. Activate Gilded Lotus by tapping it, adding three mana of any one color.
4. Activate Umbral Mantle by paying 3 and untapping it, giving itself +2/+2 until end of turn.
5. Repeat.