Warning! Spoilers King in Black: Ghost Rider #1 below
After being previously ousted as the King of Hell by Johnny Blaze's Ghost Rider, Mephisto has returned to his former throne. In the new issue of King in Black: Ghost Rider #1, Mephisto successfully makes a deal to return as the ruler of the underworld, which sees the villain back in charge of his fiery domain.
Mephisto has long been the ruler of Hell in the Marvel Universe. However, after killing Blaze during the Doctor Strange: Damnation arc, the Ghost Rider stole his throne and became the new ruler of the nether regions. But, soon after gaining the role, a group of demons rebelled against Blaze and broke free on Earth. In order to stop them, Blaze broke Mephisto free of his prison in Hotel Inferno in Las Vegas in an effort to return them to Hell. Unfortunately, the Ghost Rider soon found out that Earth was dealing with its own infection that had nothing to do with those he ruled: Knull's symbiote army has overtaken the planet.
In King in Black: Ghost Rider #1 by Ed Brisson, Juan Frigeri, Jason Keith, and VC's Joe Caramagna, Blaze (and a chained up Mephisto) search across the mortal plane for the demon sorceress Lilith. After fighting a symbiote dragon and encountering Danny Ketch as the new Death Rider, Mephisto attempts to escape and is confronted by a number of symbiote demons. Ghost Rider successfully stops them by using a powerful Damnation Stare and recovers Mephisto. However, after determining Mephisto is the best counter to Lilith and that Ghost Rider is needed to help fight among the living, Blaze reluctantly allows him to return to Hell.
Mephisto regains his throne in Hell and in his usual form, has already concocted his next evil scheme - as he brings a symbiote he promised to discard of with him down to the underworld. The comic ends with Mephisto sitting on his throne once again, while rejoicing "... it's good to be home."
Ultimately, the Ghost Rider made a deal he never thought he would make in hopes that he was choosing the lesser of two evils. The Avengers have always been able to stop Mephisto, however, Lilith's unpredictable nature made her possible ascension to the throne an impossible avenue to see play out. Regardless, letting Marvel's Devil free has got to feel like a huge mistake - even if it was the right call. Mephisto is back in Hell and it seems it's only a matter of time before he becomes a major problem again in the Marvel Universe.