Warning! Spoilers to Hellions #9 below!
It's a new era for the X-Men, but old enemies Arcade and Mastermind are still making trouble for the Hellions. Despite the majority of the mutant population on the living island Krakoa, not all of their enemies were willing to put aside their animosity and be pardoned for their crimes to work together for a mutually beneficial future. One such person appears to be Jason Wynegarde, a former member of the Hellfire Club who apparently plots against his long-time enemies despite their help in bringing him back to life. Mastermind tricks and subdues Krakoa's Hellions, their Suicide Squad of loose cannons and unpredictable mutants perfect for dangerous missions, for his associate who also has a history with the X-Men, the bow-tie wearing assassin with a flair for lethal dramatics, Arcade.
Created by Chris Claremont and John Byrne in Marvel Team-Up #65, Arcade makes up for his mysterious and conflicting origins by being an infamous assassin who kills his assigned victims with Murderworld, a playground/amusement park-themed death trap. Concerned more with playing the game over expense or winning, Arcade has tried to kill multiple Marvel heroes, including the X-Men, their allies and other X-related mutant teams. Over the years, Arcade's abilities and his upgrades to Murderworld have gotten more impressive and dangerous as he was responsible for the attack on Avengers Academy, helping Kraven's Great Hunt, and for creating the Total Recall-like simulation in Black Widow. Jason Wynegard, aka Mastermind, was created by Stan Lee and Jack Kirby for X-Men #4 and was originally a member of the Brotherhood of Evil Mutants with the ability to envelop people within realistic auditory and sensory illusions. He later attempted to join the Hellfire Club but his audition failed when trying to control the Phoenix-possessed Jean Grey lead to her transformation into the Dark Phoenix. He continued to be an enemy of the X-Men until he succumbed to the Legacy Virus.
After being brought to life thanks to X-Men's resurrection protocols, Wynegarde appeared to have reformed as he helped his former enemies fight the Cotati and Genoshan Mutate zombies during Empyre. But in Hellions #9 by Zeb Wells and Stephen Segovia, it appears he has returned to his villainous roots by targeting the dangerous X-Men team. He sets up a meeting with Mr. Sinister and takes him captive after poisoning him and later invites the Hellions to New York under false pretenses of cooperation with Krakoa and its Quiet Council. When he reveals to have manipulated the entire situation, he puts the Hellions through an intense and creative gauntlet of psychological torment that ends with the entire team unconscious. Having warmed them up, Mastermind passes the baton to his new partner, Arcade.
Over the years, Arcade has evolved beyond cheap but dangerous amusement park gimmicks to become a legitimate threat to anyone unfortunate enough to be in his peripheral. He notably upgraded both of his focus and Murderworld's possibilities in 2012's Avengers Arena when a special suit allowed him almost god-like powers within Murderworld itself, which he used trying to manipulate and kill sixteen kidnapped teenage superheroes. Although defeated, his work continued to improve and now he has Mastermind's powers, which give him access to his victims psyches and the ability to alter perceptions of reality. Mastermind is powerful enough to trick not only the Hellions but even those on Krakoa such as the Quiet Council, which makes his threat even greater.
Considering the effect his work has had on seasoned heroes like Black Widow, the Hellions are not prepared nor ready for the physical and mental horrors that await them from this deadly collaboration. The solicits for the following issue describe them being at the mercy of Arcade and a new psychological Murderworld, which will likely be a roller coaster ride the X-Men won't likely forget for a long time.