3. Thanos
Thanos is a mutant that possesses the deviant gene. Which means he mutates at a faster more evolved rate. This adds to his powers and makes him more powerful than other members of his species. In his latter years, Thanos meets the embodiment of death in female form, known as Mistress Death. Above all else he loves and worships her, which perhaps can be seen as a weakness. Thanos' quest to destroy the universe began as he obtained the infinity gems and used them to create a weapon in which he used to destroy a star system. In typical hero fashion, Thanos' arch rival Warlock attempts to stop him. However at this point, Thanos is so powerful that Warlock calls upon Captain Marvel, The Avengers, Spider Man and The Thing for help. Eventually Thanos is defeated as he's turned to stone by Warlock but not before the universe is greatly damaged. Thanos is a force of galactic proportions and is merely impossible to stop. His powers include superhuman intelligence, power, strength, agility, reflexes, speed, stamina, durability, he can time travel, is a telekinetic, has regeneration abilities and has the ability to manipulate matter and energy. And when he possesses the infinity gauntlet which holds the infinity gems, he's merely unbeatable.
His Weakness? Drax the Destroyer was created by Kronos to kill Thanos. Drax is one of Thanos' greatest foe and one of the only chances the galaxy has of stopping him entirely. Another one of his Thanos' greatest strengths is his genius level intellect when it comes to preparing for battle. Meaning, if he didn't have time to prepare, he might not pose as great of a threat during a fight. However, that's clearly a reach at best.