Reed Richards made one of Iron Man's most impressive creations look pathetic, as a version of the hero accomplished what he could not: build a Phoenix-killing machine. In Dark Reign: Fantastic Four #3 by Marvel Comics, readers learn of a version of Mr. Fantastic who used his genius to build a weapon powerful enough to kill the mighty Phoenix. Unlike Tony Stark, whose Phoenix-Killer armor was a massive failure, the Fantastic Four hero managed to stop the fiery villain on his Earth.
In the Avengers vs. X-Men crossover from Marvel Comics, Iron Man tried to take on the Phoenix by designing a massive, powerful armor called his Phoenix-Killer armor. The huge Phoenix Buster wasn't entirely ineffective, as it split Hope Summers from the incredible cosmic force, but in the end, the weapon didn't kill the Phoenix. Instead, the Phoenix Force would corrupt five heroes on Earth, leading to devastating results on Earth. Tony Stark never figured out how to crack the Phoenix, but a version of Reed Richards managed to with his god-killing machine.
In Dark Reign: Fantastic Four #3 by Johnathan Hickman, Sean Chen, Lorenzo Ruggiero, John Rauch, and VC's Rus Wooton, the Fantastic Four ends up traveling through different realities after H.A.M.M.E.R. interference messes with Reed Richards' reality-warping machine. During their multiversal adventures through time and space, Earth-5521 is revealed. In the dimension, the Illuminati unleashed the Phoenix Force on the Skrull homeworld to obliterate the planet. However, after the mission succeeded, Reed did what Iron Man couldn't do, building a machine/weapon capable of destroying the Phoenix before she fell deeper into madness.
While Reed Richards, who kills the Phoenix, isn't from the main-616 Earth, the main version of the Fantastic Four hero's access to the Bridge allowed him to return to the universe if he needed to and copy the design specs for the Phoenix-killing machine. Unlike Iron Man's failed Phoenix-Killer armor, Mr. Fantastic has a way to beat the god-like cosmic entity. He could create a machine capable of destroying the Phoenix if necessary, as his variant has the plans ready to go.
Reed and Tony have always seen each other as rivals just as much as teammates and heroes. So, the fact Mr. Fantastic could travel the Multiverse to get the designs to create the god-killing machine if needed, as his fellow genius inventor's Phoenix-Killer armor failed in such a big way, proves the Fantastic Four hero can do what Stark could not. In the end, Reed Richards' god-killing weapon bests Iron Man's Phoenix-Killer armor as his machine lived up to its name, unlike the armored hero's creation.
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