She liked messing up with the very idea of superheroes as a child even if she was somewhat intimidated with the reality. She wasn't shy or impressed by authority either.
Mouse Protector's shtick as a superhero involved playing up the silliness of it, making her opponents' defeats at her hands even more embarrassing. She found conflict addictive and this drove her needling personality in costume.
During the first meeting of her Wards team, Mouse Protector carried a shield and a sword, and wore a helmet adorned with mouse ears that she had made herself. It is unknown what her costume as an adult looked like.
Mouse Protector was a Grab-Bag Cape, her power grants her enhanced agility and stamina as well as a teleportation power where she could mark a target through touch and then teleport to them on a whim.
After Hero mentioned that he understood what someone else was saying, Mouse Protector told him that they had the serious part down before thrusting her sword into the air. She later agreed with Hero when he said that some of them were in a hurry to grow up and become heroes. After Legend arrived, he told them to be careful and said that the purpose of the Wards was about training. Mouse Protector told him that part came later and Legend told her that it would if she still wanted it then.
When Hero asked why Chevalier had sat by Miss Militia, Mouse Protector said that he probably thought she was hot and that he wanted the poontang. Reed told her not to be juvenile moments before Chevalier told her that he thought that they were similar. She asked him about it before she was told that Chevalier went after the Snatchers. After hearing the explanation, Reed told Mouse Protector that she could stop asking questions which she denied. 
Mouse Protector was ambushed by the Slaughterhouse Nine at the behest of her old foe Ravager. After her death her body was given to Bonesaw who fused Mouse Protector together with Ravager and renamed them "Murder Rat". This wasn't public knowledge.
↑ 1.01.1 ughzubat: Mouse Protector's is, yeah. Homemade-looking Wildbow: *was Wildbow: Then she was Ward for a while Wildbow: Then independent dragonkid11: WAIT dragonkid11: INDEPENDENMT!? dragonkid11: SHE QUIT!? = IRC conversation archived on Spacebatles
↑At the far end of the scale, opposite the two professional, serious looking young heroes, there was a girl with a shield and sword. Her helmet sat on the table beside her, a homemade piece of equipment with ridiculous mouse ears at the sides. It wasn’t a great helmet either; it didn’t offer enough peripheral vision, was more decorative than protective. She stood off to one side, but two others had gathered near her. She was grinning, the one who’d stood out from the rest with her over the top welcome.
And the images, the glimmers, they showed the mouse-ears girl laughing. For her companions, there was a strange writing system patterned on one boy’s skin, and the other boy swirled with a smoke that wasn’t there. - Excerpt from interlude 24.x
↑She was a composite of two ‘kitchen sink’ capes. Mouse Protector and Ravager. Two primary powers that had blended into the one, a dozen other minor powers. Flexibility, a bizarre kind of enhanced strength, reflexes and agility that had peaks and valleys, and skin as tough as leather. -Excerpt from Sting 26.3
↑Mouse Protector Could teleport to tagged people or objects. Had lesser powers including increased coordination and agility - parahumanList, bolded edit by Wildbow.
↑Prim-the-Amazing said: What was Mouse Protector's power, before she was transformed into Murder Rat?
Wildbow said: Multiple minor powers, including enhanced agility and stamina, as well as a teleportation power where she could mark a target via. touch and then teleport to them at whim. In execution, an agile opponent who could harass her opponents mercilessly, verbally and physically, where escape was impossible. - Comment by Wildbow archived on SpaceBattles
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↑ 9.09.1“Murder Rat used to be a heroine, called herself the Mouse Protector. One of those capes who plays up the cheese, no pun intended. Camped it up, acted dorky, used bad puns, so her enemies would be embarrassed to lose to her. Ravager decided she’d had enough, asked the Nine to take Mouse Protector down. So we took the job. Beat Mouse Protector, and I took her to the operating table. The other Nine tracked down Ravager and collected her, too. Just to make it clear that we don’t take orders. We aren’t errand boys or errand girls either. Now Ravager gets to spend the rest of her life with the woman she hated, making up.” - Excerpt from Interlude 11h