2) The way the Celestials used to be, I would say no. Unfortunately, like most of Marvel's cosmics, they just aren't written the way they used to be. Sometimes it seems like anyone with prep can cause cosmic types trouble. So yes, these days he'd have a good chance, unless this is two-way prep.
Both of those are prime examples of Comicbook Stupidity and extreme PIS (didnt the guy who wrote Sue destroying Exitar say something about him wanting to get revenge on the Celestials or something equally ridiculous along those lines?)...
Comicbook Stupidity and PIS are absent by default in a forum fight, and with that being the case, this is spite against Thanos...
Average showings zop; on average any Celestial (even alt reality versions of them) absolutely annihilates Thanos...
Both of us know this is true LoM. But that's just the way it is in comics. Lazy ass editors and moronic writers destroy power hierarchy and years of continuity.
So if Sue gets credit for wtfpwning one of the greatest Celestials, Reed has a gun in his closet that can wtfpwn a Celestial, they have a hyperspace weakness, etc... we should give Thanos the benefit of the doubt too.
If we throw out the PIS/CIS crap from the Fantastic Four arc, then of course Thanos stands NO chance vs a Celestial.
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..even the outer hells are indifferent matters for they bow only to potent and archaic Nodens.
Thanos was weakened while Drax used a plot device. Thanos wasn't defeated and showed he is immune to death unlike the Celestials who dropped like flies against the cancerverse's Galactus.
With prep (i.e. BOTH combatants have prep), the Celestial wins a healthy majority as well.
Usually, when a master-prepper (Reed, Doom, Thanos, etc) is seen to defeat a high-end cosmic being it is due to one-sided preparation and surprise element. But if we allow the cosmic being an equal preparation time against the "mortal" the situation is quite different.
So then why didnt Thanos defeat the Cancerverse Galactus quan? Oh cause he couldnt? This immune to death stuff is getting old. So what if he's immune to death. That just means that the celestials takes him home and has a trophy.
Thanos was in the cancerverse. The Galactus Engine wasn't where Thanos was. Lord Mar-vell was tasked with this mission. Thanos destroyed an entire universe through his actions. Powerful indeed.
He was empowered by Mistress Death. His actions set up the universe going down. Thanos was imperative for the 616 universe to prevail over the cancerverse. It wasn't the first time Thanos saved the universe.