Prototype Portal + Ugin's Nexus + Umbral Collar Zealot

Prototype Portal

Ugin's Nexus

Umbral Collar Zealot

How it works

1. Activate Prototype Portal by paying 5 and tapping it, creating a token copy of Ugin's Nexus.
2. Activate Umbral Collar Zealot by acrificing 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 Umbral Collar Zealot ability
5. Repeat each turn.

By anchoring Prototype Portal with Ugin's Nexus imprinted on it, you gain a repeatable factory for churning out the legendary artifact for five mana a turn. The secret to breaking the loop lies in Umbral Collar Zealot, which provides a convenient way to sacrifice the freshly minted Ugin's Nexus token right away. Because the Nexus replaces its own death with exile and triggers an extra turn, sacrificing the token bypasses the legend rule while securing you infinite turns and a total game lock.