Originally Posted by
whitecrown
UXM 135 specifically. Claremont was definitely inspired by a lot of things even if all those influences never made it onto the page explicitly. I've also read theories that Mastermind was under control of Shadow King and the Muir Island Saga would have revealed that the Dark Phoenix Saga was essentially put into play because of him. Small hints like how Proteus was unable to affect Mastermind with his reality warping powers (even though there's no way Mastermind would be immune to that on his own), how Mastermind was able to fight Cyclops in a psychic duel on the astral plane when his powers never enabled him to do that, or even how an essentially braindead or vegetable Mastermind was alive again for UXM 175. All of it makes more sense if the Shadow King had always been in control of him and brought him back for the From the Ashes storyline that introduced Maddie. I think this was also when Destiny was having visions of a being outside reality although maybe that was supposed to be the Beyonder and not Shadow King. But it's pretty telling that in one of the What If? issues where Phoenix was still alive and depowered, Mastermind is haunting her to take her power. Eventually it turns out that Mastermind's body is just a dead husk being controlled by Shadow King who is the real threat and Phoenix is able to destroy him for good in battle.
One thing I noticed is that while everyone portrays Phoenix with cosmic fire powers these days, in the 1970s, the only fire that seemed to come into play was her manifesting a fiery raptor. Even then, it seemed to be psionic in nature because it never burned characters with flame and Jean never was shown throwing fire from her hands like the Human Torch. It seemed like her powers were all energy-based (Claremont called her an energy manipulator in X-Men Forever) as Phoenix was a being of pure energy and life incarnate. Hence why the M'Kraan Crystal starts to absorb her because she's not flesh and blood anymore and it takes Storm and the other X-Men to keep Phoenix tethered to humanity and not fully absorbed. I think she only starts burning people in Dark Phoenix but even that might not be fire as much as pure cosmic energy that burns Storm and the other characters. Even when she manifests the Phoenix Raptor in UXM 135 before departing for the stars, there's a whole explanation about how she used the lightning from a storm to do that.