The M on Vegeta's forehead stands for Majin. It is a seal put by Babidi to indicate that he controls Vegeta in a certain way. It was placed through black magic. He knew that he was powerful enough to resist mind control. He then goes on an indiscriminate killing spree to provoke Goku to fight him.
As his final selfless act, Majin Vegeta self destructs in order to save Bulma, Trunks, Goku and the entire world from the threat of Majin Buu, despite knowing that unlike Goku, he wouldn't keep his body after death. This marked the final transformation of Vegeta from his selfish evil and neutral state into a good hero.
The Majin Brand
The emblem is a seal of the evil wizard family's magic. Those branded with the mark gain incredible power, augmented by either wizard's dark enchantments. However, the price of this strength often means those possessed are left under the control of the wizards, with their inner evils being brought out.
Majin Vegeta's powers were on par with Super Saiyan 2's, which means a Majin transformation doubles a Saiyan's attributes. Vegeta also seemed fully capable of harnessing every last bit of power, as if he knew his limits all along without prior training.
They were equal in strength, ONLY AFTER THE MAJIN TRANSFORMATION. Again, ONLY AFTER the transformation. even so, Goku was still stronger in the long run.
Furthermore, in the only current relevant comparison, Ultra Ego Vegeta seemed to damage Granolah more than Ultra Instinct Goku. With all the evidence and inferences fans have available currently, it seems like Ultra Ego wins out in the strength department.
According to the latest manga of dbs, there are still forms of ultra instinct left for goku to achieve, like the one which grand priest uses. And ultra ego is still just the same as it was before. Even though in power, UE wins.
All full-blooded Saiyans (such as Raditz, Kakarot, Vegeta, Nappa, Paragus, Broly, or Bardock) have names that are a pun on various vegetables.
In his Super Saiyan God state, he is a match for Hit at full power. During the final fight against Goku Black and Future Zamasu, Vegeta was able to attain the form and access it at will much like Goku.
Vegeta reached Super Saiyan 2 while training during the 7 year gap after the Cell Games. Vegeta has become more powerful than Gohan was against Cell.
Buu eventually awakens and is taken to New Namek to confront Moro. During the fight, the Grand Supreme Kai takes control of Buu's body and it's revealed that Buu once had god ki, but it was destroyed when the pure Majin Buu was killed by Goku.
After being defeated by Goku and the Z Fighters, Vegeta eventually settled down on Earth as he trained to surpass Goku and become the mightiest Saiyan in the universe. This rivalry would lead him to embrace his own inner darkness years later and transform into the evil Majin Vegeta.
1 1) Defeated by Goku
While Vegeta seemed to be stronger, Goku was able to overpower him with the Kaioken technique. It all leads to Goku and Vegeta unleashing their strongest attacks. This forces Goku to increase his Kaioken to x4, giving him the push to defeat Vegeta.
This chapter confirms that Vegeta considered his life-long employment under Frieza (the man who committed planetary genocide against his people) to be his greatest regret. In fact, Vegeta broke down in tears at the thought of spending his whole life helping the being who killed his entire race.
It's possible that Majin Vegeta was strong enough to keep pace with Goku while he was still just a Super Saiyan 2, but it's clear that, if Goku had transformed again, he would have easily beaten the Prince of Saiyans. Which this knowledge, Vegeta seem less impressive as an opponent and even as a rival.
But, thanks to an ancient ritual, Goku was able to power up to Super Saiyan God and then, he fought Beerus. Their fight came very close to destroying the entire universe but somehow, they managed to end it with the Earth still intact.
Gohan's strongest power transformation is Gohan Beast, an evolved form of Gohan's Potential Unleashed state which originated from the awakenings he has experienced since childhood.
Half-Saiyans (1/2 Saiyan, 1/2 Human) resemble both Saiyans and Humans. They have the skin color of tan variants, and varying eye and hair color. They can either be male or female.
Gohan Beast is Gohan's most powerful new form. Unlike the more straightforward Super Saiyan God forms, this one is based on Gohan's more animalistic transformations that he had as a child.
Frieza cannot expect to defeat a God of Destruction who can casually destroy halves of planets on the tap of his fingernail. Plot armor had always affected Beerus' strength, and it's probably not a great idea to buff Frieza so much that he can casually go toe-to-toe against the likes of Beerus.