With the prep Reed gets samples of his DNA, his profile, and everything.
This is the man that Onslaught admitted would have toppled him had he been given time. That man that defeats the Black Celestial (I think? I know he does take out some celestials and fights the Black Celestial through time. I forget). He's defeated Magneto, Dr. Doom and other foes that are more formidable than Mongul. He has nullified Hulk. HULK.
There is no blitzing a prepped Reed and time is his advantage not Mongul's. One could ask: "How is Reed gonna harm *insert name here*" and yet he comes out on top.
Maybe something as simple as forcing Mongul to lose the will to fight:
As seen in Civil War, Reed can become quite obsessive with his work til the point it almost killed his marriage. The likelihood of Reed's communication skills being good enough to sweet talk Mongul are unlikely. Mongul may be brute, but he is also smart and will know if Reed is being sincere about his feelings. Mongul will not suffer heart break again, or else this be the result of their date:
Indeed. Obsessive enough to beat Mongul by prepping non-stop.
I suspect if that prep includes developing some sort of alien compatible viagra supplement, then maybe Reed can win. These intergalatic beast (like Mongul) are not much different from foreign dictators, eager to get their rocks off, trading secrets and political favors with the US for viagra pills (AntiHero knows what's up).
HeyHey: Cable Vs. Anti Hero:Despero; poor cable ZeN:Dr. Doom (prep) Vs. EnoughSaid: Shadow King; Doom with prep is just one of the most combinations in the universe, with an iron will and whatever device he fashions up, he'll take this one. TimmyD:Mr. Fantastic (prep) Vs. Loneshot: Mongol; close, but Reed's imagination and genius can answer the question of how is he going to damage this brick. MagicC:Flash Vs. Jailblazers: Iron Man (prep); too fast; there are plenty of ways i can imagine tony with prep winning, but i just can't see him getting them off. El Kabong: Jean/Cyclops (prep) Vs. Raiderfan:Maestro (prep)[; does anything really need to be said?
There should be enough tech on Asgard to work with. Reed isn't familiar with magic but I'm sure given enough prep time he can get familiar enough with the objects and materials provided to him on that plane.
This doesn't also include the fact that he is a master tactician, and psychological profiler. He can defeat Mongul in Asgard, there will be enough for him to work with. Even if it's just picking up one of the mystical weapons they have there and figuring out the best plan to execute it.
Though he has many great physical feats, his intellect is also considered a power of his. He is one of the smartest in the Marvel Universe, showing himself to be even as smart as alien civilizations. Because of this, mind control is useless, though when it does affect him, it wears off more quickly than on an average human. He is not flawless however, as he has tried many times to revert the Thing back to his normal human form. He also indicates that he can not understand magic. Later in life, he also earned a Black Belt in Judo.