Thor & Beta Ray Bill vs Mr Majestic
Thor/Beta Ray Bill-Enormous Superhuman strength, speed and endurance, extremly long life-span; also, via Mjolnir, the ability to fly, control weather and fire force blasts.
Mr Majestic-Strength, speed, flight, eyebeams, genius level intellect, micro vision, ice breath, ability to survive in space and is invulnerable to conventional weaponry.
It depends.
There are certain iterations/variants of Thor that would totally annihilate Majestros. For example when he has the god/odin-force etc etc etc.
On the same vein there are some depictions of Majestros that have him moving entire solar systems and being an exceedingly cunning nigh invincible warrior with amazing resources (in terms of Kheran wartech) and even surviving to the end of the universe and becoming what is basically God (not a small 'g' god, but big G level).
BRB is actually quite consistent in how he is written. No matter who is penning him he is always shown as an extremely powerful exceedingly capable warrior/cyborg/horse-face alien/Norse-power imbued/Storm-breaker wielding being.
It depends.
Some potrayals would have Thor Girl (yep, there is one) messing up Majestros, while others would have Majestros laying waste to the whole of Asgard, Hades and Valhalla.
Depends.
NB: The major difference between Superman (even Pre-Crisis Superman) and Majestros (who, when well written, does feats that are basically Pre-Crisis Kal-L/Kal-El and not post-crisis Kal-El) is that Superman is amazingly vulnerable to magic-based attacks. Eg a punch from Captain MArvel (Shazam) does him for a loop, and thus a blast from Thor's Mjolnir or BRB's Storm-breaker would mess Superman up bigtime due to the magic.
Majestros doesn't share that weakness .....not that Magic will do nada to him, just that it is not quasi-kryptonite as magic is to Superman.