Ash Beast's power is not fully understood, but relies on a conversion between mass and energy to constantly surround himself with some kind of explosion. He seems to possess a regenerative ability and exhibits partially uncontrolled shape-shifting. His explosions are comparable in power to the destructive capabilities of an S-Class threat.
Has a shapeshifting beast form generated through constant matter/energy and energy\matter conversion allowing him to replace and rearrange parts of himself. This kept him far healthier then he should have been. He could absorb fire and presumably other forms of energy to augment his form.
Ash Beast was shown to be capable of matching Scion for an indeterminate period of time. In that fight, he was able to regenerate even as Scion tore into him.
Ash Beast triggered in Matruh, Egypt and has been roaming around Africa ever since. As he traveled on foot, people could see him coming from miles away. As a result, by the time that he reached a settlement, it had been evacuated.
People tried to control Ash Beast, to steer him in the general direction of their enemies, though it rarely worked for long.
Khepri created a bubble in range of Ash Beast before using Doormaker to create a portal so she could exert her control over him. She had Trickster bring Ash Beast through the portal before sending him against Scion. Ash Beast and Scion started to tear into each other as Khepri pulled her front-line capes back. Khepri sent other capes to assist Ash Beast including one that fed fire into his body.
↑ 1.01.1Ash Beast Shapeshifting beast form generated through constant matter to energy and energy to matter conversion Independent Breaker Changer - Parahuman List; bolded edit by Wildbow
↑ 2.02.1Creating a portal to give me access to it was troublesome. Others had tried to control it before, to steer it in the general direction of their enemies. Warlords, villains, masterminds. It rarely worked for long. When working with power on this scale, chaos had a way of trumping order. Too much energy disrupted the portals. - Excerpt from Speck 30.5
↑ 3.03.1I reached out to Ash Beast, a living force of nature. It had originally triggered in Matruh, Egypt, and had been roaming since, making its way across Africa. All of the destructive power of any class S threat, tempered by the fact that it usually traveled on foot, and people could see it coming from miles away. When it reached a settlement, that settlement was usually evacuated.
An unending explosion, a rolling mass of fire and smoke with a person at the center. Here and there, it took physical form. Whether it was the fire or a massive leonine claw that tore into the ground, it produced the debris, dust and ash that was its namesake, driven along the ground by the perpetual storm of fire. - Excerpt from Speck 30.5
↑Bringing him through a doorway was hard. He generated so much heat, and while his shape and form were malleable, they weren’t wholly under his control. - Excerpt from Speck 30.5
↑ 5.05.1I moved a forcefield cape to the Ash Beast’s location, and then created a bubble, putting it in range of the being. I made a portal within the bubble. More forcefields encased the bubble on my side for safety’s sake. My power operated through the forcefield, and the connection formed.
I identified a young man, at the center of it all, and I could now think of the Ash Beast as a ‘he’ instead of an ‘it’. He was surprisingly healthy, but he had a power that kept him in good physical condition, a natural breaker-class adaptation that came with his power. Energy to matter and matter to energy. - Excerpt from Speck 30.5
↑ 6.06.1They appeared behind Scion. Glaistig Uaine distracted, with one ranged cape hitting Scion full-on in the face, another feeding fire into Ash Beast’s body. - Excerpt from Speck 30.5
↑ 7.07.1Shaping the fire, driving it out to the sides.
Shaping the flesh. From energy to physical form. Wings. Catlike legs to spring into the air.
The Ash Beast lunged into the air, above the water, and he streaked towards Scion like a comet. The forcefield cape followed, to maintain the connection.
I moved Alexandria, Legend, Moord Nag and the others on the frontline through doorways as the Ash Beast struck the golden man. Golden light tore into flesh that had been forged of fire, and more flesh was created to replace it. The Ash Beast tore into Scion, and the flesh was replaced just as quickly. - Excerpt from Speck 30.5
↑The portal was wiped out. Without any barrier in the way, the beam radiated forward to wipe Ash Beast, the cape with the pole, Trickster, and Othala from existence. - Excerpt from Speck 30.5