The Phoenix Force has a had a large number of hosts throughout its history in the Marvel Universe. While this has granted immense galactic powers to some of Earth’s heroic X-Men and Avengers, it also sets them up to become dangerous universal threats.
To be sure, Jean Grey and the Phoenix’s most recent host, Echo, have proven to be dangerous hosts to its immeasurable power, but neither of these women compare to the most terrifying host: Emma Frost. But why exactly did The White Queen’s time with the Phoenix Force represent a dire threat to the entire universe?
The Phoenix Force imbues its host with cosmic-level power, but also tends to elevate the inherent emotions (and especially the innate darkness) of the host. As mentioned above, other hosts struggled with this drawback and often gave in to vengeful, fiery temptation. There is no greater example of this submission than in “The Dark Phoenix Saga” from Uncanny X-Men #129 through #138 (by Chris Claremont and John Byrne). The storyline depicted Jean Grey’s fall from a heroic Phoenix into a terrifying planet-destroying force of nature.
There are several reasons why Emma Frost’s time with the Phoenix trumps even the vaunted “Dark Phoenix Saga,” though. Emma may not be as powerful a telepath as Jean Grey, nor is she in any way telekinetic, but she was amplified to a massive, superior power level after absorbing only a fifth of the Phoenix Force. During the events of the Avengers vs. X-Men crossover, Emma quickly proved to be absolutely ruthless. As she gained more power, she quickly began to lose control of her furious impulses, lashing out and turning the others against one another.
Using her powers, Emma began to forcibly read the minds of her fellow mutants. She even located people who’d murdered mutants across the world and enacted awesome displays of brutal vengeance.
Emma’s use of the Phoenix Force is not limited to the main MU, though. An alternate reality portrayed in What If…?: Astonishing X-Men (by Jim McCann, David Yardin and Ibraim Roberson) saw Emma sacrifice the Stepford Cuckoos to attract the Phoenix Force. This amplified the psionic remnant of the villainous Cassandra Nova within Emma’s mind. Fully unleashed and controlled by Nova, Emma used the cosmic power to destroy an entire world before returning to Earth. After murdering fellow X-Man Beast, Emma barely regained control before she was killed by Kitty Pryde / Shadowcat.
The Marvel Universe version of Emma Frost, of course, was originally an enemy of the X-Men before she joined the team. She never tried to fully atone for her villainous past and simply found new purpose as a teacher and team leader. Even though she was now a hero, Emma never lost her ruthless nature that helped her stand out amongst her teammates. It makes sense then that the Phoenix Force took advantage of Emma’s emotional vulnerabilities and rapidly transformed her into a truly monstrous host. Any universe with a Phoenix-Emma Frost combination is likely set for a lot of death. Echo’s current time as host is certainly a concerning and dangerous development. However, Emma’s time under its influence — in any reality — remains the worst possible possibility for the Phoenix Force.
from Ultimate Comic Blog