Here's the breakdown:
Within Marvel Comics:
* The One Above All: The ultimate creator of the Marvel Multiverse, he stands above even the Living Tribunal.
* The Beyonder: A being of limitless power from another dimension, capable of wielding reality-altering forces.
* The Chaos King: An embodiment of chaos, capable of devouring entire universes.
* The Celestials: Powerful cosmic entities, each possessing vast power, but likely not individually able to beat the Living Tribunal.
* The abstract entities: Beings like Eternity, Infinity, and Death are powerful but their domains are specific. They might be able to challenge the Tribunal, but a definitive victory is unlikely.
From DC Comics:
* The Presence: The ultimate creator and source of all power in the DC Universe, akin to The One Above All.
* The Monitor/Anti-Monitor: Beings of near-infinite power, capable of manipulating reality on a grand scale.
* Perpetua: A powerful cosmic entity who created the multiverse, but likely not on the same level as The Presence.
Key Points:
* The Living Tribunal's power is vast, but it's not infinite. He is constrained by his role as a judge and is bound by the cosmic laws.
* Most battles are about context and circumstances. If the Living Tribunal is willing to fight and isn't restricted by his role, he becomes a very formidable opponent.
* There are beings in both universes who are more powerful than the Living Tribunal, but they might not be willing or able to defeat him.
In Conclusion: While the Living Tribunal is one of the most powerful beings in the Marvel Universe, he is not invincible. There are several entities, both within and outside of the Marvel Universe, who could potentially defeat him. However, it's a complex question with no easy answers.