First of all, we totally have a Story Forge v8 now, and it's nowhere near autosaging. It can be found here: >>119870. But hey, since I'm here, I'm gonna give you a hoof with your idea, Anon.
Allow me to be perfectly honest. The fact that you explicitly refer to your protagonist in the first person does not fill me with confidence. Self-inserts are generally frowned upon, in my experience. But I'll look past that. About the idea itself. Your requirements for this character of yours are: capable of building a dimensional portal, being athletic enough to evade Princess Celestia, and "psychotic." This combination of traits is a little odd, but at least your character has a definite flaw. I think the direction to take the character is obvious: make him a mad scientist.
Here's my interpretation. The character (let's call him "Professor Pandemonium) has already conquered the world and laid its heroes to waste. He's got an army of robots working to maintain the world's governments and enforce his rule. He's completely victorious, and he's bored out of his mind. So Pandemonium invents the DouR to find a new world to conquer or, at the very least, find someone new to talk to. Upon his arrival in Equestria, he is offered a kind hoof and a place to recover from the injuries he sustained from the fall by Celestia. However, Celestia is quickly possessed by some kind of demonic force from his world who's similarly bored and hoping to frame her. Pandemonium escapes and does battle with the possessed Celestia, aided by the Great and Powerful Trixie. The battle ends in a draw, and subsequently, Pandemonium and the demon go their separate ways. Pandemonium, vowing revenge on Celestia, begins to assemble a Legion of Doom, Equestrian Division to overthrow Celestia. And bam, there's your story.
Actually, this is starting to sound interesting. If you'd like a creative consultant, feel free to contact me at email@example.com.