Warning: contains spoilers for Heroes Reborn #4!
Guardians of the Galaxy's Rocket Raccoon just became even more powerful than Knull, aka the fabled King in Black, who only recently came within a hair's breadth of annihilating Earth and plunging the galaxy into eternal darkness. Rocket's insane power-up takes place in the new reality of Heroes Reborn, in which Mephisto has tampered with the timestream so that the Avengers never became heroes, instead replaced by the Squadron Supreme.
Heroes Reborn #4 - from Jason Aaron, Ed McGuinness, and James Stokoe - explores Rocket's attempt to take down Doctor Spectrum, the ultra-powerful wielder of the Power Prism. Patterned after DC's Green Lantern, Doctor Spectrum can use his prism to manifest energy constructs that have allowed him to take down major threats like Thanos, the Super-Skrull, and even the Inhumans. In this reality, Rocket is the galaxy's greatest bounty hunter, and a coalition of alien races hire him to kill Doctor Spectrum, whose attempts to prepare space for American colonization have cost countless lives.
While Rocket's Groot-enhanced gun is able to hurt Doctor Spectrum, the powerful space enforcer quickly breaks free from its effects, attacking Rocket in earnest. It's then that Rocket shockingly gains the powers of the Starbrand, finally putting the two on an equal footing. The Starbrand is one of the most powerful forces in Marvel Comics - a planetary defense system that can empower one individual to protect Earth from cosmic threats. It turns out that while the Squadron Supreme thought they'd disposed of the Starbrand in the Negative Zone, a young child bearing the brand was later rescued from space by Rocket, and now she's sending him the power he needs to take on Doctor Spectrum.
Of course, all of reality has been bent to make the Squadron Supreme Earth's Mightiest Heroes, and Spectrum himself shows he's near to Knull's power level. Many of his foes are imprisoned in Knowhere - a severed Celestial head that Doctor Spectrum says he claimed to show the cosmic beings that in this reality, there's only one god, and He's American. In Marvel's true reality, Knowhere was created by the King in Black, who likewise beheaded a Celestial as a show of strength.
The Starbrand wasn't available during the King in Black event due to being possessed by a baby, but the child seems to have aged in Heroes Reborn's reality, and is able to give Rocket Raccoon the power to put up a fight. Unfortunately, Doctor Spectrum still wins the day, using a weaponized Cancerverse - an eldritch universe conquered by unspeakable horrors - to incapacitate Rocket. Spectrum then grabs Rocket, shoving him "headfirst into a supernova to get him to talk," observing that, "for the first few hours, he doesn't say anything, except for some of the most colorful uses of profanity I've ever heard in any quadrant."
While Rocket is eventually killed by Doctor Spectrum, his ability to survive when literally pressed against the surface of the sun shows that with the Starbrand's power, he's stronger than the King in Black. In King in Black #5, Venom finally destroyed Knull with a surprisingly similar tactic, pushing him into the sun, where he quickly broke apart. Knull lasted for seconds in this situation, while Rocket sadly endures for agonizing hours, only giving up once Doctor Spectrum inadvertently threatens to kill the true Starbrand by blowing up his ship.
It's a grisly fate for Rocket Raccoon, though thankfully the true Starbrand is quickly recruited by the growing group of heroes fighting to fix reality, led by Blade and Captain America. While the King in Black was eventually revealed to be a little less than the god he claimed to be, Rocket's brush with power was still one for the ages, showing that while it's limited to the specific role of protecting Earth, the Starbrand remains one of the greatest forces in the Marvel Universe, limited only by the wielder's imagination. Hopefully, the true Starbrand can help fix the timeline and bring Rocket Raccoon back to life, as Heroes Reborn continues.