Monn

Monn is the main antagonist of Core: Afterlife (Part 1) and a supporting character in Core: Afterlife (Part 2). He sports a fantastical design in Part 1, a spikey coat and a mechanical set of wings that serve only to intimidate. Please note that this profile contains spoilers!
For the majority of Part 1, Monn is a background force that causes trouble without being seen yet. It is only in the final act of Part 1 that Ossa is able to locate and confront Monn, and only after he reveals himself. Monn's goal involves ripping a hole in reality to bring the realms together, allowing armegeddon to start as the worlds of the living and the dead fuse and become one, disrupting the balance of life and death. Monn nearly accomplishes this task, the realms being visually available to one another before Ossa interrupts his efforts to allow them to physically collide. His motivations are not revealed in Part 1, and he refuses to touch on the subject when Ossa pushes in attempts to befriend him instead of fighting. Their clash is heavy, with Ossa having gotten so powerful from the onlookers, she's able to easily sweep Monn under the rug. However, she proves to be too powerful, decapitating Monn with her newly unveiled demonic magic, his realization of her nature coming just before he is snuffed out.
With his first afterlife over, Monn is reborn in the 2nd realm of the afterlife, with a similar body, but now with new unseen scars. Monn takes this setback in stride, but continues to fear Ossa for months after. He figures she will follow, seeing as she knew she wasn't supposed to kill him (his aspirations are still fully achievable in the second realm of the afterlife, after all), and prepares himself to fight her again - this time he knows he can win. With Ossa lacking her friends, her powerups will be few and far between, and Monn had time to become stronger himself.
By the time Ossa finds Monn, he's made tremendous progress in his second attempt to open pathways between the realms, and his strength and tact has brought him to a much better place in terms of his next clash with his demon adversary. Their initial clash is no contest, as Ossa does nothing but struggle to maintain control in the fight, and Monn seems to be having fun. As swiftly as the fight began, however, it ends - a strange force interrupting their battle.
The Angel Aetherra appears, speaking to Ossa directly and completely ignoring Monn. However, Monn overhears that Aetherra intends on killing him for Ossa, and then killing Ossa. Fearful for their lives, Ossa and Monn both help one another in fleeing, escaping the gaze of Aetherra in an abandoned house with demonic symbols painted on it's doors, built high into the sky and only accessible via Monn's jetpack. That night, Ossa and Monn hunker down and stick together, knowing it would be unwise to split up now. Monn finally opens up after Ossa expresses her guilt and anquish over killing him, and explains his motivations to open the realms - his daughter who still lives. Monn doesn't tell her much more, but Ossa seems incredibly grateful to have finally heard his story from him, and explains that she thinks their best option for survival would be to team up. Monn rejects the idea, and the two go to sleep. In the morning, Monn relents and accepts their alliance, explaining that Ossa is likely the one of them that will be able to defeat Aetherra, but only if she is powered up by friends. Ossa agrees, and the two leave the safety of the house in pursuit of powering up Ossa further.
They are almost immediately intercepted by Snofori, a soldier of Aetherra's. The spirit is daunting, seems unstable, and holds no expressions on his face but sadness and remorse. Ossa tries to avoid conflict, but Snofori simply doesn't listen and attacks. Monn and Ossa team up incredibly well, holding off the attacker despite him being far stronger than either of them. In the fight, Monn's jetpack is completely destroyed, reduced to metal scraps, removing the option of their safehouse for future use. Ossa continues to attempt to befriend Snofori, and manages to get him talking after he disables Monn. Snofori opens up a little about his situation, that Ossa cannot help him from Aetherra. However, he expresses gratitude that Ossa listens and shows him compassion, and agrees to spare them... for now.