MTG Combo: Gilded Lotus + Kurkesh, Onakke Ancient + Manifold Key

This generates infinite mana and infinite taps/untaps of another artifact.

Tap Gilded Lotus for 3 red mana, activate Manifold Key's untap ability and pay an additional to copy it for Onakke Ancient. One untap ability targets Gilded Lotus, the other Manifold Key itself. This nets you one red mana. You can repeat this until you get infinite red mana, and then you can just get any colour of mana after that.

Edit - Manifold Key cannot target itself so this combo does not work.