WARNING: The following contains spoilers for Thor #10, by Donny Cates, Nic Klein, Matt Wilson, and VC's Joe Sabino, on sale now.
In Thor #9, the God of Thunder, seeking answers about his hammer Mjolnir and the source of Asgard's failing magics, once again traded places with his human alter ego, Donald Blake. A long time ago, Dr. Blake was a human being created by Odin to teach his son humility. Whenever the two would switch places, Donald would then be living a peaceful life in a magical dimension that was created just for him -- a place where he had no perception of time.
However, as Asgard's magics began to waver, Donald became aware of the time he spent in what he would come to call his prison -- and he grew mad. Now, a murderous Donald Blake has finally been freed, and he's ready to declare war on Thor and the rest of Asgard. To make matters worse, he now has the power of not one but two legendary figures that make him a literal force to be reckoned with.
In Thor #9, the God of Thunder smashed his hammer on the ground, a magical act that frees Donald Blake and that traps him in the blissful dimension of his human alter ego. However, what Thor found was not the idyllic world of before -- now, it's a place consumed by death and destruction. Bodies are littered on the ground, the victims of a man who succumbed to madness. In the series' latest issue, Thor continues to explore Donald's home, and he comes across another one of his victims -- but this one isn't human: it's actually the Midgard Serpent.
The Midgard Serpent, aka Jormungand, is a magical creature of Asgardian legend. It is a massive, snake-like monster that Thor has tangled with before. Here, however, Thor finds the Serpent nearly dead. It explains that once the magics of Asgard began to fail, he was finally able to cross over into Blake's dream world. There, he sought a potential ally in him. The Serpent offered Blake some of his power so that they would become allies -- but in his madness, Blake took it all.
Worse, the power of the Midgard Serpent isn't all that fuels Donald. Indeed, Jormungand tells Thor that when Blake took his power, he also discovered the power of the Odin-Force within himself. After all, the human was created by the former All-Father. He is a byproduct of the Odin-Force, which means he has some of that magic -- some of that power -- inside of him. By unlocking it, Donald combined this power with that of the Midgard Serpent -- something which allowed him to defeat Jormungand, leaving him near death in his dreamland.
With these two powers combined, Donald Blake has no match. He now has the abilities of two immensely powerful Asgardian legends, which makes him more powerful than Thor.
Thanks to this massive power boost, Donald Blake is able to destroy Asgard's armies and now, he has traveled to Earth. There's no telling what his plans are just yet, but with the magic at his disposal, he could do unimaginable damage. It's clear he intends to take his revenge on Thor, which means Donald will likely attack Midgard, the realm the God of Thunder cares so much for. But he may not stop there -- next, he could turn his attention to all ten realms currently under the protection of the new King of Asgard.