WARNING: The following contains spoilers for Ghost Rider #7 by Ed Brisson, Aaron Kuder, Jason Keith and VC's Joe Caramagna, on sale now.
Ghost Rider's coming war with Lilith for control of hell has been dragging in countless magical and demonic forces, setting up a battle of massive proportions. Now, one of the most dangerous demonic forces in the entire Marvel Universe is prepared to join the fray -- and fight alongside the heroes.
Blackheart just offered his services to Ghost Rider in his battle against Lilith and he's going to force that alliance if necessary.
After taking the throne of hell from Mephisto, Johnny Blaze has found himself increasingly corrupted by the demonic forces around him and that he's been combatting. With his intentions becoming more and more destructive, he even drags Mephisto with him when he goes to confront Doctor Strange for his role in the events that led to Johnny taking over hell in the first place.
Meanwhile, Lilith is able to use the chaos to her advantage, convincing all the demons in New York to attack Blaze and Mephisto while they're distracted, in exchange for their own hellish domain if she's able to take over hell in their stead.
Blaze quickly overwhelms Doctor Strange despite Strange's best efforts to quell his rage, but is stopped by the alliance of Wolverine, Punisher and Danny Ketch (who has gained the Spirit of Corruption to replace the Ghost Rider powers Blaze stole from him). The group is able to save Strange from Blaze's wrath and Ketch is even able to absorb much of the demonic influence inside Blaze, restoring him to his senses.
While Blaze (and a bound Mephisto) head off so Blaze can complete a new mission, Ketch returns to the Fadeaway to find his loved ones captured by Blackheart -- who demands a team-up to bring down Lilith.
Blackheart is the "son" of Mephisto, created from centuries of accumulated evil. Blackheart is an incredibly powerful demon and the Prince of Hell, set to inherit the throne when Mephisto formally vacates it. His modus operandi is to attack heroes throughout the Marvel Universe and tempt them, hoping to corrupt them and doom their souls.
He's been a frequent enemy to multiple incarnations of Ghost Rider, while also commiting himself to corrupting heroes like Spider-Man and Daredevil. He's been frequently shown to be ambitious, perhaps overly so -- often leading him to underestimate his targets and only end up dragged back to hell by Mephisto. He was even once sent to Earth to learn humility, similar to how Odin banished Thor to the planet.
With Mephisto off the throne and Lilith trying very hard to claim it, Blackheart might see his best chance at taking the throne. Ghost Rider may be more powerful than him, but he's also made it clear he has no desire to rule eternally.
Meanwhile, Mephisto might never be this weak again. If the heroes are able to put Mephisto back into a position where he could claim power, Blackheart would stand to succeed him and likely would do anything he could to ensure that he did. It's also very on-brand for Blackheart to suggest a team-up by taking his hopeful partner's closest loved ones hostage. Blackheart could be a very useful agent in the coming battles, especially with most of hell wanting and willing to work with Lilith. It's just a matter of watching out for his inevitable power play.