Warning! Spoilers to Heroes: Reborn American Knights #1 below!
Although his vendetta against the Avengers likely motivated Mephisto's Heroes Reborn reality, it hasn't stopped Marvel's version of the Devil from concocting a special hell for Daredevil. Having long had issues with Daredevil's costumed appearance and religious morality, Mephisto reimagined Matt Murdock as a faithful priest for the religion that worships him. His costumed identity as the Saint has him battling those who follow his God's example, creating a painful conundrum that chips away at Murdock's sanity which likely brings a smug smile to Mephisto's face.
With Matthew Murdock's religious upbringing, he is familiar with angels and demons which comes in handy when his career as the crimson vigilante Daredevil has him dabble in the supernatural. In Kevin Smith and Joe Quesada's Guardian Devil, he meets Marvel's devil, Mephisto, who reveals that he knows him, "He who would call himself a devil and do the work of the just." Murdock's methods clearly infuriate Mephisto. In Heroes Reborn, the world has been reimagined without the creation of the Avengers with countless lives redefined especially heroes who operated as or fought alongside Earth's Mightiest Heroes. In this reality, Mephisto is not only the person responsible but has replaced God with his own churches, statues, and servants praising him and his works.
In Paul Grist, Chris Allen, and Marc Derring's Heroes Reborn: American Knights #1, Commissioner Luke Cage and Detectives Misty Knight and Jessica Jones' investigation into the Saint's brutal campaign against criminals lead to the Church of Mephisto. They meet with cleric Matt Murdock who swears on Mephisto's honor that all of the Saint's victims are regular patrons of the church. When Murdock murders one of the Saint's victims, Commissioner Cage later tries to intervene during a tense standoff between Matt and the police at the Church. Despite his personal feelings about religion, Luke tries to talk to the tormented Murdock who not only reveals he is the Saint but that he couldn't stand hearing the guilty confess their sins only to continue the cycle of violence and evil instead of changing their ways. " I had to show them a better way," he said deliberating how his belief in justice conflicted with his religious devotion to acting how Mephisto would.
The entire situation is the kind of infernal pettiness and manipulation that one would expect when someone's earned the ire of the Devil himself. Mephisto does not like that Matt Murdock tries to be a hero in his image so when he has a chance to rewrite everything, he couldn't resist getting a little revenge. Matt is now a clergyman similar to his absent mother but for a church dedicated to the Devil. He can't handle absolving guilty men so Mephisto allows him his own version of Daredevil, showing how hard he's fallen when he shows no reservation in killing his enemies, a crime that Daredevil is paying for over in the main Marvel Universe. The final twist of the knife is confessing his crimes and beliefs to Commissioner Cage, reimagined as a Christian man, while still questioning his love and devotion to Mephisto, a god who has unknowingly condemned him to a lifetime of suffering.
While Mephisto has his reasons for making the Avengers suffer, his torment of Daredevil is simply because he couldn't stand the idea of good being associated with the devil. Matt's suffering ends when he falls victim to a bullet intended for Commissioner Cage but Mephisto's immortality could mean that his suffering could only be taking an intermission. With Heroes Reborn concluding, time will tell if Mephisto's vendetta against Daredevil will continue or if he'll be distracted with causing other Marvel heroes pain.