Burnscar's mental state was influenced by her power; if she didn't use it, she would become depressed, but the more she used it the more reckless she became. She felt guilty about the things she had done when she wasn't using her power, and would use her power to escape that feeling.
Her test for prospective members of the Nine was to force them to face their greatest fear, although that wasn't always possible.
One of Burnscar's treasured memories was talking with Labyrinth at the Parahuman Asylum when they were both having good days. She saw Elle as a friend. Burnscar didn't seem to notice when the girl was sarcastic.
Burnscar wanted to come to the Bay in order to meet her former friend Labyrinth, but she didn't want Labyrinth to actually join the Slaughterhouse Nine, as she was very fond of Labyrinth and didn't wish for her to be corrupted or put in danger of being killed by Burnscar or any other member of the Nine.
Mimi is a pyrokinetic who can teleport herself freely through flames and becomes increasingly psychopathic the more fire she is using. She is also completely fireproof.
Mimi's pyrokinesis is extremely versatile. She created concussive fire blasts capable of knocking over the Undersiders and Bitch's Dogs, shot twin flamethrower-like streams of fire from her hands, and sent fire "snaking" across water. She shaped her fire into foot-high images of characters in her comic books and of her memories while reading. She could put out her fires at will, create walls of fire, and leave burning footprints that widened into a trail of fire. She could also throw fireballs that could punch holes through walls by summoning fire to her palms and hurling it.
Using her power adjusts the chemical balances and connections in her brain to reduce her empathy, impulse control, and emotion, so she "can’t help" using her power if there’s fire nearby. This creates a cycle where Mimi is increasingly unlikely to stop using her power the more she uses it.
Mimi's eyes glowed orange when she activated her power.
Bonesaw also modified members of the Nine with various "safeguards"; sheathing their vital organs and major arteries in a protective sub dermal mesh, further wire reinforcement was put into the skeleton to avoid broken bones, with special attention was paid to the organs and spine to keep them functioning. She also rendered her teammates resistant to her pathogens, and granting them artificial neurons which allowed them to make plans Cherish could not see, it is unknown if this could be adapted for other Master powers.
Mimi was a patient at the same asylum as Labyrinth. She looked back on their conversations as treasured moments, and saw her as a friend, although the guards used Elle as an enticement to make her cooperate. When Labyrinth was freed by Faultline’s Crew, Mimi escaped as well, spending some time on the streets. 
When she used her power to scare off a pimp who was harassing her, she lost control of her emotions, killing him and trapping herself in a feedback loop. Shortly thereafter, the Slaughterhouse Nine found her during one of her psychotic episodes. With her conscience and empathy being suppressed, she found them good company, by the time Mimi cleared her head however she had a kill order.
↑“You’re not really in a position to be making demands,” Trickster said. “You’re bleeding to death, and we do have the ability to hurry the process along.”
Cherish shrugged. “Bonesaw gave me the works. Mesh sheaths for every major artery and organ, wire reinforcement for my skeleton. It’s not going to kill me anytime soon.”
I made a mental note of that. Chances were good that Jack, Bonesaw and the other more vulnerable members of the Nine had some similar protection. How differently would things have played out if Ballistic had used his power and blown them up?
“I could,” Trickster threatened. “Or we could wait and see which happens first: Either you agree to share the information we want or you slowly bleed out.”
“A game of chicken? I’m down.” Cherish prodded her injury with a fingertip. It was clear it hurt, but she still stuck a finger into the hole and investigated some. “The auto-injection pump is dosing me with painkillers and antibiotics now. First time feeling this stuff work.” - Excerpt from Snare 13.7
↑ 9.09.1“A benefit of little Bonesaw’s smoke,” Jack answered. “If I recall correctly, it’s something of a safeguard in case she accidentally deploys a concoction she hasn’t immunized herself or the rest of our team against. The fact that it works against bugs and small rodents is a side benefit, rather than the intent. Bonesaw’s work has made us members of the Nine more or less immune to disease anyways.”
“And the gunshot?”
“Subdermal mesh. There’s more protection around the spine and organs, and you landed that shot pretty close to my spine. It hurts quite a bit.” - Excerpt from Prey 14.10
↑Jack paced back and forth, two or three steps at a time, gesticulating with his knife. “I was looking forward to Cherish’s attempt. Bonesaw and I even had a plan in mind. I wanted to see what she did, how she worked around Siberian’s immunity to her power… then the safeguards Bonesaw implanted in us would have kicked in and released us from her thrall, and oh, the look on her face. To have seen that would have been so very worth all the trouble. And that girl just spoiled it all.”
Jack was getting heated, talking mostly to himself. “That was the whole point! To see how long we could go without tipping her off. Bonesaw helped with some surgery, even some artificial neural connections that Cherish wouldn’t be able to see. So much work and preparation ruined.” - Excerpt from Plague 12.4
“Jack’s rules, not mine. But fine,” Burnscar said. Something about the tone in her voice: it sounded casual, but there was something in it that reminded me of Shadow Stalker and Sophia. It wasn’t angry like Shadow Stalker was, but it had the same emptiness. I just hadn’t really picked up on it in the past.
Burnscar gave Mannequin a hand in getting to his feet. Cracks marred his lower body, and his left arm was a mess of cracked ceramic and pale gray organic pulp. I heard her murmur something.
Mannequin shook his head. Burnscar said something else.
He raised one hand, and Burnscar slapped it in a lazy high-five.
She turned towards us. “There. He just tagged me in. Forfeited his turn.”
She cracked her knuckles, and every flaming piece of debris on the street became a pillar of fire, stretching vertically for the sky. The fire snaked over the surface of the water to cut off our avenues of retreat.