Last year, Marvel's House of X and Powers of X reshaped the world of the X-Men in some seismic ways, but not everything about the X-Men's new world order makes sense yet. One of those elements is Theresa Cassidy, the hero who served X-Force and X-Factor as the high-flying Siryn or Banshee.
While she's never been the most prominent mutant, her presence on Krakoa raises some big questions about the nature of Krakoa's mutant resurrections.
The issue surrounding Theresa has its roots in 2012's X-Factor #238-239, by Peter David and Leonard Kirk. In this story, Havok gets a call about people being killed by high-pitched sonic vibrations in Ulster, New York, which makes Theresa a prime suspect. Theresa and Havok travel to find the real culprit behind the murders, subsequently clearing her name in the process.
On their mission, Theresa encounters the Morrigan, an Irish Goddess with a bone to pick with her. The Morrigan taunts Theresa for taking a name that mocks her and attacks her after the mutant refuses an offer to join her. Thanks to a tip from Morrigan's sidekick, Jezebel, the new Banshee and Havok take down the Morrigan, However, Jezebel leaves Theresa with an ominous warning about walking with gods or being crushed by them in a coming apocalypse.
After that warning rattles Theresa, she begins having visions of her dead father, the X-Men's first Banshee, which tell her that the Morrigan was merely testing Theresa earlier.
As her powerful teammate Polaris has a particularly dangerous breakdown, Theresa and her teammate Layla Miller summon the Morrigan. When they ask the Morrigan to save Lorna Dane, the god tells Theresa that she'll have to do it herself.
After two millennia as a goddess, the Morrigan is ready to step down, tired of answering the prayers of the world. To stop Lorna from disrupting Earth's magnetic field, Banshee accepts the Morrigan's offer and takes her place becoming the new Morrigan.
Armed with the power of a goddess, Theresa easily helps Lorna. She also appears to Jamie Madrox to tell him that she is no longer the woman he knew, though she admits she has always loved him and knows he felt the same for her. Although she says that its time for both of them to move on, she tells him to pray for her if he ever needs any help.
After the coming apocalypse that Jezebel warned about comes true, Jamie was transformed into a demon. This causes stress to his marriage with Layla Miller, who is pregnant with his child. At his most desperate moment, Madrox prays to the Morrigan, who appears to him and helps him return to his human form.
Before House of X #6, this was the final appearance of Theresa Cassidy, who presumably remained as the Morrigan in parts unknown. However, Theresa can be seen as the X-Men gather to celebrate their new mutant homeland in House of X #6, where she uses her sonic scream powers to fuel Dazzler's sound-powered light show.
In this scene, Theresa appears to be in her traditional, more human appearance. However, it's not clear how this happened, since being a deity isn't something that one can just stop doing. This means that in between her last appearance and House of X, the Morrigan either died and replaced herself with another woman in some unseen story or that Theresa was brought "back" via the resurrection protocols.
While the Krakoa resurrection protocols specifically ban the resurrection of mutants who aren't confirmed to be dead to keep this problem from happening in the first place, this could mean that there are technically two Theresa Cassidys running around -- the Morrigan and the more human Theresa on Krakoa. After all, so few characters really know what happened to Theresa in X-Factor to begin with.
Assuming that Theresa didn't just stop being the Morrigan in some unseen adventure, Theresa's predicament raises another possibility that could have greater implications for the rest of the X-Men.
For now, it doesn't look like Theresa's conundrum will be addressed, since she's not slated to have a regular role in any upcoming X-titles. While the implications of what really happened to Siryn could mark another foundational shift in the X-Men's world, the questions that Theresa's presence raises may not be answered anytime soon.
In reality, the Morrigan plot was likely forgotten by Marvel's writers, but the idea that there could accidentally be two of the same mutant in the universe as a result of the nature of the "resurrection" procedures is certainly intriguing.