From planet devourers to Asgardian fire giants, the Marvel comic book pantheon has a wide variety of monsters from all dimensions. Some of these beasts are inspired by real-life legends. For instance, Ymir and Surtur are both derived from Norse mythology while Mephisto is inspired by Biblical depictions of Satan.
Considering Marvel's over-the-top nature, these monsters all possess truly extraordinary powers that showcase their physical as well as mental strength and expertise. Not all of these monsters are inherently antagonistic though, as can be seen from Galactus and Hulk's storylines.
Hulk
After Bruce Banner was exposed to gamma rays, he awakened the beastly side that is Hulk. The green-skinned monster channels his rage to wreak large-scale destruction. His fists can crush vehicles and spaceships and he has proven his mettle by defeating strong enemies like The Thing and Wolverine. If not flight, jumping across great distances comes naturally to him. With every landing, his jumps can create impactful sound waves.
Some of his lesser-known powers include resistance to psychic control and growing stronger with more radiation. These diverse abilities coupled with his iconic strength have allowed him to combat threats not just on Earth but even on other planets and outer space as could be seen in the 2000s Hulk comic issue Planet Hulk.
Marvel Zombies
The Marvel Universe has its fair share of superpowered heroes. When the same heroes turn into raging flesh-eaters in the horror comic Marvel Zombies, they still retain these powers, making them an extremely strong collective of evil monsters.
Hulk's appetite for destruction. Wolverine's regenerating factor and adamantium claws. Scarlet Witch's Chaos Magic. Captain America's hand-to-hand combat skills. When put together, the Marvel Zombies can showcase many strong powers to defeat various kinds of enemies. The monstrous angle comes from the fact that these zombified heroes are driven by rage and carnivorous tendencies, making them more feral than usual.
Morg
Morg serves as one of the Heralds of Galactus. When his master grants him cosmic powers, Morg ends up defeating former Heralds like Silver Surfer with minimal effort. Apart from enhanced speed, stamina, and agility, Morg is also able to manipulate cosmic energy to project space energy bolts. He also carries a double-bladed ax that can result in waves that can destroy spaceships and even leave a crack in Galactus' ship.
A dip in the Well of Life augments his powers further as he becomes the strongest Herald in the Universe. Hence, he proves to be a worthy pawn in the hands of Galactus. In general, he is also increasingly durable as he has proven his ability to survive in outer space without any food or sleep. This ability might be present in Hulk and a few other zombified Marvel heroes but not all of them, giving Morg the upper hand.
Thanos
Thanos can naturally control all dimensions once the Infinity Gauntlet lies in his hand. But aside from this, he is very much capable of going head-to-head against mighty intergalactic heroes like Silver Surfer and Thor. The Mad Titan has a lot of powers similar to the Eternals given his mutant-Eternal heritage but he also goes on to gain mystic abilities bestowed by Death herself.
Telekinesis, telepathy, and interdimensional travel are other common powers associated with Thanos. But what also makes him special is his cerebral supremacy. Proficient in virtually every field of science, Thanos is also an expert strategist. So, even though others like Hulk and Morg might possess brawn, Thanos's brain would be an added bonus to overpower such creatures.
TIE: Ymir
Ymir, the Ice Giant, is a Thor comic book villain and an ancient being that gave life to other Ice Giants. True to his physical form, he can generate extreme cold to freeze his foes to death. Additionally, his height of at least 1,000 feet makes him one of the strongest and durable giants.
His fights with Surtur and Odin have also ended in a stalemate, establishing his immense superhuman strength, and healing factor. Ymir also doesn't need to care about death as his healing factor allows him to regenerate from anything that is related to ice (even if it is a particle of ice). This regenerative factor allows him to overpower even Eternals like Thanos as he has existed way many years than him.
TIE: Surtur
Surtur is a fire demon who is often depicted as one of Thor's most powerful villains. The horned giant is a gargantuan figure with a height of over 1,000 feet. As for his powers, Surtur is shown to be on par with mighty Asgardians like Odin himself.
As for his tryst with fire, he often generates extreme heat and his powers seem to increase in front of the Eternal Flame. Armed with the Twilight Sword, he is also capable of channeling dark magical energies. The sword has allowed him to break dimensional barriers and even inherit Odin's powers for a brief while. When compared to the Ymir, most of Surtur's fights with the Ice Giant have ended in a stalemate as their energies cancel each other out every time they have clashed.
The Mangog
Mangog's power emerges out of the hate of billions and billions of humans and gods in the universe. Since negative emotions like hate and anger are in abundance, the Mangog has no dearth of fuel to get stronger. He can take down collective forces of Asgardian warriors and once even defeated the trio of Odin, Thor Odinson, and Jane Foster (as the newest version of Thor).
Thor and other characters often have to resort to magic tricks to defeat him as weakening him in a physical battle is a Herculean task. Mangog never received any combat training but his energy manipulation and dependency on sin are such that he can prove to be an unstoppable force. Even the best of opponents can show signs of rage and this is what weakens them in front of Mangog who thrives the most on rage.
Mephisto
Mephisto is the personification of the Devil in the Marvel Universe and possesses powers that stem from dark magic. Superhuman strength and shapeshifting come naturally to the immortal demon who is also resistant to injury.
Apart from the physical powers, his mental powers are also worth noting. Just like the other depictions of Satan in pop culture, Marvel's Devil often makes deals with other characters and manipulates their memories to do his bidding. Once this manipulation works on powerful heroes like Ghost Rider, chaos is unleashed. In Silver Surfer: Judgment Day, he even goes against Galactus. Even though the latter gains the upper hand, he still proves to be a worthy competitor.
Tyrant
Tyrant was a living machine created by Galactus. Hence, apart from cosmic powers, his bio-mechanical roots also allow him to psionically control any and all forms of technology. Matching many of his powers, Tyrant instantly turned into a tyrannical warlord believing in conquering the rest of the universe and devouring planets. However, unlike Galactus who just engages in these activities for survival, Tyrant's actions border on wanton violence.
While fighting his creator, both beasts prove to be equally strong until galaxies start getting destroyed. At the end of the day, it was the weapon Ultimate Nullifier that killed him instead of any other Marvel hero. Other creatures like Mangog and Thanos might be powerful but even they can't single-handedly destroy galaxies.
Galactus
A creature that consumes entire planet systems is bound to be Marvel's most powerful monster. He was once a mortal man but his present form makes him a god-like figure that drains living planets off their energy.
Galactus channels a force known as the Powers Cosmic that allows him to create interdimensional portals, manipulate souls, resurrect beings, and destroy multiple solar systems at once. So, as he can exert control over whole planets, it is highly unlikely for any one of these planet-dwellers to defeat him in direct combat. His power is also administrative as he has managed to subdue other powerful 'Heralds' under him like Silver Surfer and Morg.