WARNING: The following contains spoilers for Secret X-Men #1, now on sale from Marvel Comics.
Marrow's mutant powers are unique and unconventional even among the X-Men. Her mutant ability causes her bones to grow at an accelerated rate, manifesting bone spikes that poke through her skin. Over time, Marrow has learned to control her bone growth. She can command her bones to grow into spears which she snaps off and uses as weapons, or into defensive armor. She can even direct her bone protrusions to grow into aesthetically pleasing shapes for cosmetic purposes, like she did for her Hellfire Gala outfit. Most recently, Marrow has tested the limits of her mutant ability to make a functional bone spacesuit.
In Secret X-Men #1 (by Tini Howard, Francesco Mobili, Jesus Abertov and VC's Clayton Cowles), Sunspot assembles an X-Men team to meet Empress Xandra and Deathbird in space and prove to them that the X-Men can be trusted as their allies. Sunspot chooses Marrow as one of the X-Men for this mission. When their spaceship is attacked by Sidri bounty hunters, the other X-Men on the team put on spacesuits and get ready to fight in outer space - all except Marrow.
Instead of wearing one of the spacesuits created by Forge, Marrow creates her own spacesuit made of her bone growths. The bone spacesuit keeps her alive in the vacuum of space and she fights off the bounty hunters alongside her teammates. Marrow has always been a reckless and daring individual, and her use of the bone spacesuit exemplifies this. She admits that she isn't sure whether or not the bone spacesuit will actually function in space, but since she can easily be resurrected on Krakoa if she dies, she is eager to try out the bone spacesuit untested.
The sense of safety that the Resurrection Protocols gives Marrow emboldens her to risk her life unnecessarily. She is not afraid of dying, because she knows she can be brought back by the Five. This knowledge encourages her to take bigger risks than she would normally take and experiment with using her mutant powers in ways she never would have imagined before.
Even before Krakoa's Resurrection Protocols, Marrow was particularly creative when using her mutant powers and continued to find new ways to incorporate them into her life. Though she initially weaponized her bone growths by simply snapping off sharp pieces of bone growing out of her body and using them as knives and spears, she later learned to manifest large bone tendrils from her body, which she could control and use as weapons while they were still attached to her body.
Marrow has also used her bone growths as a fashion statement. When she was on the X-Men in the 90s, she shaped her bone growths to form a kind of tiara attached to her forehead and also incorporated the bones into her costume. As a member of the Morlocks, mutants who were rejected by humanity and took pride in the ways they were different from humans, Marrow's mutant identity is extremely important to her. It comes as no surprise that she would want her physical appearance to reflect her mutant identity and her specific powers.
Marrow's invention of the bone spacesuit is not the first time she has used her powers to create something to wear, but it goes a step beyond her past experimentations with her powers in how dangerous it is. Given that Marrow is happy to risk her life on a whim as long as she knows she can be resurrected, it's possible that she will continue experimenting with her powers in even more innovative and dangerous ways.