Warning: The following article contains spoilers for Uncanny X-Men #20, by Matthew Rosenberg, Salvador Larroca, Guru-eFX and Joe Caramagna, on sale now.

The '90s were good for the X-Men. Thanks to the blockbuster successes of Chris Claremont and Jim Lee's X-Men, Rob Liefeld and Fabian Nicieza's X-Force and X-Men: The Animated Series, Marvel's mutants became generational icons with a multimedia empire. That era also saw the creation of fan-favorite stories like the Age of Apocalypse as mutants flourished throughout the Marvel Universe.

RELATED: Marvel Reveals Major X's Mother Is This Iconic Mutant

However, things aren't going too well for the X-Men right now. With most of the team trapped in the Age of X-Man, Cyclops and Wolverine have pulled a handful of veteran mutants to form a rag-tag X-Men team in a world that hates them more than ever before. While they've been trying to take care of the team's enemies once and for all, the X-Men have seen an unusually large number of their allies and enemies die in recent months.

While the un-reformed villain Emma Frost and the mutant-hating General Callahan have been behind most of their troubles, the X-Men encountered some of their deadliest '90s villains, the Upstarts, in Uncanny X-Men #20.

Uncanny X-Men Upstarts Return

While following a lead on the Nasty Boys, the X-Men discover that those minor villains have been killed by Fabian Cortez, Trevor Fitzroy, Siena Blaze and Shinobi Shaw. Collectively known as the Upstarts, those once-prominent villains lost a brief, brutal battle with the X-Men that ended with Shaw's apparent suicide.

Although none of the Upstarts have appeared in a decade, the team has always been especially lethal. Throughout the early and mid '90s, the Upstarts participated in a mutant-killing competition for an undisclosed prize. After that story ended unceremoniously in 1994, each of the Upstarts gradually faded into obscurity.

Fabian Cortez is arguably the Upstarts' most famous member. With the ability to increase other mutants' powers to dangerous levels, Cortez formed the Acolytes, a group devoted to Magneto's mutant superiority philosophy. Shortly after his debut in Claremont and Lee's X-Men #1, he seemingly killed Magneto and the other Acolytes. A few years later, a resurgent Magneto killed Cortez for his betrayal, and it's not totally clear how or when Cortez was resurrected.

RELATED: X-Men: Unproduced Beast Solo Movie Details Revealed

The return of Trevor Fitzroy, the Upstarts' deadliest member, is also somewhat mysterious.

Originally from the same future as the X-Men's Bishop, Fitzroy is a serial killer with the mutant power to generate time portals by absorbing the life-force of his victims. During his debut in Lee, Whilce Portacio and John Byrne's Uncanny X-Men #281, he killed the Hellfire Club's Donald Pierce, his cybernetic Reavers and most of the Hellions, Emma Frost's young mutant team. Fitzroy was eventually killed by Bishop, but his presence in this issue could be explained by his time-traveling powers.

The presence of Siena Blaze, who has violent electromagnetic abilities that allow her to teleport, is also unexplained. After being introduced with a handbook-style entry in the Stryfe's Stike File by Scott Lobdell, Fabian Nicieza and Brandon Peterson, Blaze fought X-Force and the X-Men before briefly serving as a hero in another universe. She died and briefly returned as a zombie in 2010's "X-Necrosha" crossover.

RELATED: Marvel Unveils New House of X, Powers of X Character Designs

When Shinobi Shaw was introduced in X-Factor #67 by Lee, Portacio and Claremont, he seemed like the future of the Hellfire Club. With the ability to alter his density, he seemingly killed his father, Sebastian Shaw, and attempted to reshape the Hellfire Club in his image.

Shinobi Shaw death

Once the rest of the Upstarts were defeated in this issue, Shaw accuses the X-Men of working for Emma Frost, who recently formed a new Hellfire Club. After bragging about keeping himself and the Nasty Boys out of Frost's control, Shaw uses his powers to make his hand intangible, plunges it into his head and solidifies it, killing himself instantly.

As the X-Men turn their attention to Frost, Callahan and more pressing matters for the remainder of the issue, the return of the Upstarts and the death of Shaw both go unmentioned.

With House of X and Powers of X set to dramatically redefine the X-Men's world in a matter of weeks, the brief return of several forgotten villains pales in comparison. However, in a X-Men story that began with Cyclops and Wolverine returning to their famous '90s costumes, the Upstarts serve as another callback to the X-Men's most popular era.