Warning: contains spoilers for Avengers #51!
As Marvel's new Phoenix comes into her true power, Avengers has revealed the Marvel characters capable of killing X-Men's cosmic force of destruction, with four major names that will be familiar to fans of the MCU. Following the Avengers' Phoenix Tournament, Echo - aka Maya Lopez - was chosen as the Phoenix's new host, but having learned from prior hosts who fell to its influence, she's working hard to keep it under control.
As Echo works to suppress the urge to raze the planet after facing the Dark Phoenix of another reality, she's using the Avengers' Celestial base to assess the beings capable of destroying the cosmic force. But while Black Panther initially suspects she wants this information so she can train against potential threats, Maya reveals that she's under no illusions about the danger posed by the Phoenix, and actually just wants to know how to kill it should the moment come when the Phoenix Force once again threatens her home planet.
After facing off against the Dark Phoenix of the Multiversal Masters of Evil in Asgard (where she's been unwelcome ever since Thor learned that the Phoenix Force considers him its son), Echo is reminded how out of control her powers could grow, and Black Panther offers her the Celestial database so she can use her photographic reflexes to enhance her abilities. Echo asks the Celestial base to display, "all beings with the power to kill the Phoenix," leading to some surprising results.
The database identifies Thor, Scarlet Witch, Thanos, Odin, Galactus, Molecule Man, the Living Tribunal, and the Beyonders. The latter inclusions make sense as part of Marvel's cosmic ecosystem, as the Living Tribunal is second only to the One-Above-All, and the Beyonders' power is near limitless (partly as they're often treated as a metaphor for Marvel's writers.) Molecule Man will be a somewhat surprising inclusion for those who haven't kept up to date with Owen Reece's more recent adventures, which have made it clear he occupies a unique place of power within the multiverse. Galactus makes sense as a being who is capable of killing the Phoenix Force in a battle which could ultimately go either way. Similarly, All-Father Odin - who served with the Phoenix on the Avengers of 1,000,000 BC - would probably only be able to slay the firebird at incredible cost to himself, and even then only at the height of his power.
Thanos' inclusion is more questionable, partly because his powers tend to fluctuate from story to story, though it's backed up by the fact he has survived combat with past Phoenix hosts, such as his son Thane. It's likely the Phoenix Force is just as (if not more) capable of killing the Mad Titan as vice versa, but Thanos' incredible power is always coupled with his genius intellect, evening up the suggested conflict. Scarlet Witch will be a particularly surprising inclusion for fans, though her role in Avengers vs X-Men made it clear Chaos Magic has particular power over the Phoenix Force. Finally, casual readers may be shocked to find Thor on the list, but it's worth keeping in mind he recently underwent a huge upgrade after killing Galactus - it's possible this is the reason he makes the list, though it's worth noting that his victory over Galactus may mean he's capable of this feat with his regular powers.
X-Men comics have always suggested the Phoenix Force is a nigh-omnipotent being in Marvel lore, but Avengers has clarified that some surprising heroes are actually capable of killing it outright. As rumors of mutants joining the MCU continue to build, X-Men fans will be taking note that Thor, Odin, Scarlet Witch, and Thanos are apparently powerful enough to slay the Phoenix in Avengers comics.