SPOILERS AHEAD!
Powers of X #4 brings us back to the multiple timelines, including an important flashback to the first year of X-Men. Magneto and Xavier visit Mr Sinister, presumably before he intersects with the X-Men. Here are some important back issues that feature some of the key ideas in this issue.
Bar Sinister
The issue opens in yet again another island retreat: Bar Sinister. We’ve firstseen Bar Sinister in Hickman’s Secret Wars #2. This appearance makes it the first of its kind in this reality.
Glam Sinister
This “glam” version of Sinister also was seen in Secret Wars, though Kieron Gillen really introduced that version of Sinister, and his multiple clones, in his Uncanny X-Men run. Uncanny X-Men (2nd series) #14 is a great showcase of this version as the X-Men lay siege on his hideout. You’ll notice as well the motif of a full red diamond used to distinguish the “real” Sinister from his clones.
Sinister’s Library
The concept of Sinister’s library of DNA was first discovered by the X-Men in X-Men (1991) #34.
Sinister Secrets
If previous installments of Powers of X slowed down significantly in back issue references, this one makes up for it in spades. The “Sinister Secrets” graphic was loaded with cheeky references. Here are some of our best guesses for what they refer to:
#2 : Jumbo Carnation
This reference of mutant trendsetter cut down in his prime could refer to Jumbo Carnation, a mutant fashion icon introduced (and killed) in New X-Men #134.
#3: Madelyne Pryor
Madelyne Pryor is a clone of Jean Grey created by Mister Sinister, who is most likely the “deceased redhead pretender” refered to in this entry. She first appeared in Uncanny X-Men #168, was revealed as a clone in Uncanny X-Men #240 and died in X-Factor #38 (An alternate reality version later appears throughout various X-Books).
#4: Captain Marvel
The last thing we’ve seen washed up on the shores of Bar Sinister was Captain Marvel, during Secret Wars #5 and #6, though other theories consider that perhaps the mutants from the previous future life of Moira MacTaggart (Rasputin, Cardinal, etc) were sent there after being engulf by Xorn’s black star.
Revealed #1: Thunderbird
This is an easy one – John Proudstar was of the “All-New All-Different” class, but was killed soon after in Uncanny X-Men #95. Thunderbird’s powers were a fairly generic augmented strength.
#5: Wolverine, Jean Grey, Cyclops, White Queen
There are many love triangles (among other shapes) in X-Men comics, but none are more prominent, and more of interest to Sinister, than Cyclops and Jean Grey and their relationships with Wolverine and Emma Frost. This entaglement comes to a head in Morrison’s New X-Men, with the Frost/Cyclops affair beginning in New X-Men #138 and Wolverine and Jean Grey come together in her final moments in New X-Men #150.
#6: Ernst
Ernst is the probable “progerian mutant” with ties to sinister. She makes an alliance with Sinister to get a new body for her friend Martha in Spider-Man and the X-Men #6. Sinister is an important villain in this fun series.
#7: Vulcan
The Summers brothers have been under Sinister’s microscope for most of their life, and are undoublty the pair that “jumped out of a plane”. The story of the third Summers brother was first teased by Sinister himself in X-Men (1991) #23.
It was revealed in X-Men Deadly Genesis that Vulcan was the third Summers brother. Deadly Genesis also has a familiar plot of the long-held secrets of Charles Xavier.
It was teased, however, to be Adam-X, who was featured in X-Men (1991) #39.
#8: First Horsemen
This is a relatively new reference, as Hickman’s contribution to Marvel Comics #1000 was a story of Apocalypse and his first Horsemen.
Revealed #2: Inferno
This one references a previously mentioned event: Inferno (where Madelyne’s story comes to a head).
Inferno is coming out of Mister Sinister after years of dealing behind the scenes, and is essential reading if you want to learn more about this classic X-Men villain.
#10: Cassandra Nova
The certain “bald someone” could be Xavier, though there is also his twin sister Cassandra Nova. This theory gets even more interesting considering the parralels between Xavier and Casssandra, and the practically mirrored scene from her introduction in New X-Men #114 and Xavier sporting the same hat as he introduces Cypher to Krakoa.
Sage
Sage was previously seen in House of X, though is specifically mentioned as an integral part of Krakoan communications in this issue. Though she was undercover as “Tessa” in the Hellfire Club, she joins the X-Men in the X-Treme X-Men series.
Interestingly, X-Treme X-Men deals with Destiny’s diaries. Considering her knowledge of Moira’s many lives, it will be interesting how Hickman deals with this era of X-Men.
Trinary
Trinary was more recently introduced in the excellent series of X-Men Red. She is another member of the Krakoan communications team.
She first appears in X-Men Red #1 and is more formally introducted in X-Men Red #2.
Black Tom
Black Tom Cassidy is a more complicated character. What is of interest in this character is his treelike appearance he first gained in Deadpool (1st series) #3 and featured in Generation X #25 (which could be an important read, considering Hickman’s fondness for this team). You also have Bastion and Mondo in this that last issue, so it’s definitely worth a read!