Necrogenesis + Void Attendant + Ashnod's Altar + Chromatic Orrery

Necrogenesis

Void Attendant

Ashnod's Altar

Chromatic Orrery

How it works

1. Activate Necrogenesis by paying 2, exling a creature card from an opponent's graveyard and creating a 1/1 Saproling creature token.
2. Activate Ashnod's Altar by sacrificing the Saproling, adding 2.
3. Activate Void Attendant by paying 2 and putting a card from an opponent's exile into their graveyard, creating a 1/1 Eldrazi Scion creature token.
4. Activate Ashnod's Altar by sacrificing the Eldrazi Scion, adding 2.
5. Repeat.