Prototype Portal + Ugin's Nexus + Extruder

Prototype Portal

Ugin's Nexus

Extruder

How it works

1. Activate Prototype Portal by paying 5 and tapping it, creating a token copy of Ugin's Nexus.
2. Activate Extruder by sacrificing the Ugin's Nexus token.
3. The Ugin's Nexus token is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
4. Resolve the Extruder ability, putting a +1/+1 counter on a creature you control.
5. Repeat each turn.