Prototype Portal + Ugin's Nexus + Bartolomé del Presidio

Prototype Portal

Ugin's Nexus

Bartolomé del Presidio

How it works

1. Activate Prototype Portal by paying 5 and tapping it, creating a token copy of Ugin's Nexus.
2. Activate Bartolomé del Presidio 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 Bartolomé del Presidio ability, putting a +1/+1 counter on it.
5. Repeat each turn.

By anchoring Prototype Portal to a previously imprinted copy of Ugin's Nexus, you gain the ability to churn out cheap token copies of the legendary artifact for five mana a activation. Whenever you use Bartolomé del Presidio to sacrifice that token, Ugin's Nexus's own replacement effect intercepts the graveyard to exile it instead, successfully bypassing the "legend rule" while triggering an extra turn. This creates a self-sustaining loop that grants you infinite turns and leaves Bartolomé del Presidio growing larger with every iteration.