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1) In her future timeline, Rachel was kidnapped and programmed into serving as a mutant tracking “hound”. The spiked leather outfit (originally colored pitch-black) was the regular outfit for these hounds and was first seen in Rachel’s memories. Along with the conditioning Rachel received so-called facial “hound marks,” though later on she used her powers to mask the scars/tattoos. However, when her concentration slipped they were visible. [Uncanny X-Men #189]
2) When she joined the X-Men, Rachel had no codename or costume. Instead, she wore civilian clothes and several different versions of leotard outfits.
3) It was only after she decided to take on the Phoenix moniker, in honor of her mother, that she started to wear a costume to match the name. [Uncanny X-Men #199, Uncanny X-Men Annual #9]
-) After Rachel returned from the Mojoverse and joined Excalibur, she openly wore her Hound outfit, apparently as a sign that she had overcome her troubled past. [Excalibur: The Sword is Drawn]
4) When Rachel was mortally injured, the Phoenix Force took her body into space, wearing the green Phoenix costume (of Phoenix II) again. Once Rachel’s health was restored, she decided that this costume didn’t feel right, so she changed it to the color scheme used by Dark Phoenix. [Excalibur (1st series) #64]
5) At one point Rachel entered the timestream and wound up 2000 years in the future. There she grew old and founded the Askani Sisterhood under the name Mother Askani. Rachel was again wearing her Hound costume, but on top of it a purple robe.
-) With the Askani timeline erased from existence, Rachel again found herself in the timestream, wearing the Dark Phoenix costume once more.
6) Adopting the name Marvel Girl to honor her mother, Rachel now also wears an outfit that is a homage to one of Jean Grey’s Marvel Girl outfits: a green, tight miniskirt and a green and yellow T-shirt, leaving a bare midriff, combined with yellow boots and yellow glasses reminiscent of Jean’s yellow pointy mask. Rachel has, however, admitted that she isn’t all that comfortable in that outfit, which isn’t her usually style at all. When she uses a lot of her power, her shadow form reappears along with a tiny golden Phoenix symbol over her left eye. [Uncanny X-Men #444]
7) After her uniform was destroyed dealing with the Blade of the Phoenix, Rachel conjured up a new costume. It is primarily a set of black leather pants and a tanktop, exposing her arms and bare midriff. The top has a stylized orange flame design covering most of the front, and similar orange cuts adorn the sides of her hips. She also wears black boots and armbands, and a brown 'X' belt around her waist. [Uncanny X-Men #481]