Morspallidum's origin story

Morspallidum was the bastard child of Aterpestis, ruler of a realm with minor connections to ours. Even to he was born out of marriage, he was the only viable heir to the throne. That was, until the lords wife, Venorsanguino, gave birth to his step-brother- Umbra. Morspallidum was furious, as a mere child took away his honest rights to rule over the realm. One night, he approached the child, sleeping in his bed. Morspallidum smothered Umbra in his crib, just as his father came in. Furious, saddened and shocked, Aterpestis couldn't bring himself to slay his own seed. He instead banishes Morspallidum into the plains of the multiverse. As Mors grew, so did his powers. Soon, he was able to create matter from nothing. At least he thought it was soon. Back in his realm, 3 generations of lords had passed. But he didn't. He only grew stronger, learning the very secrets of life and death. Anyone can die, with some effort. Except for him... He found a desolate universe, one without any signs of life, and he shaped it to his liking. The small realm became a forest filled with his minions and small rodents. After a certain time, a young girl entered the universe. Morspallidum didn't care, for one child couldn't harm his realm. But when the portal under the rock was discovered, a group of mortals coming in, that was the last straw. He now prepares a force to destroy Earth and reshape it. Question is- will you just let him, or will you fight back? Or, will you... join him?