thing about mordru is he kind of has plot armor like Thanos. That said classic Mordru's feats were just down right silly at the best of times and grossly abusive towards other top tier characters at best. Even post nerfing he's still a contender with the Wizard Shazam while he's standing at the Rock of Eternity and even then to my understanding it was a temporary nerf and he will still be the one to consume all the lords of order and chaos and basically be super rapeface uber.
Mordru is leagues above Atum and other beings, it's like he is the combine form of Dormammu, Odin, Mephsito, Zeus and these beings would probable tickle Mordru at best, and they are powerful as hell.
Even though I think Mordru would win, in Classic Demogorge's favor, Athena said the Pantheons had better get their act together and oppose the Skrull Gods or Demogorge would devour the Earth Pantheons (because they'd be obsolete).
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..even the outer hells are indifferent matters for they bow only to potent and archaic Nodens.
Odin will shitting in his pants against a being like Mordru whos powers and abilities are greater, Mordru defeated Shazam in ROE, and Shgazam is Odin equal, he defeated Nabu who is consider the most powerful Lord of Order Mordru counterpart and he is more deadly than all the Hell Lords put together.
Mordru is the Lord of Chaos and destined to be the last one standing, he has no beginning, his magic is arcane and powerful as hell, he sbsorbs all forms of magic and energy, he feeds on it. He has absorb all the magic out of one Universe, absorbed all the power of a Lord of Order and Chaos, he can attack beings from another dimension like he did against LOH. As much I like Atum, Mordru is beyond Atum period.
I wouldn't say Mordru is really a Lord of Chaos/Order in the grand scheme of things his goals don't really fall into line with one or the other. He generally doesn't go out causing havok for havok's sake. Also in the end he will absorb all the Lords Chaos/Order. It would have been interesting to see him do so before the reboot just to see how writers would portray him knowing that it would all be wiped clean so even if they created a retardedly powerful character with no peers it would all be gravy anyways.