Prototype Portal + Ugin's Nexus + Megatog

Prototype Portal

Ugin's Nexus

Megatog

How it works

1. Activate Prototype Portal by paying 5 and tapping it, creating a token copy of Ugin's Nexus.
2. Activate Megatog 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 Megatog ability, giving it +3/+3 until end of turn.
5. Repeat each turn.

This clever loop bends time by turning the replacement effect of Ugin's Nexus into an endless engine of extra turns. Because tokens hit the graveyard momentarily before ceasing to exist, sacrificing the token copy created by Prototype Portal triggers the Nexus's exile clause, neatly bypassing its legendary restriction while safely granting you an extra turn. Meanwhile, Megatog serves as the willing executioner for the artifact, ensuring the token goes to the graveyard on command while growing massive in the process.