I like all of these ideas. And yeah, sorry about that. He's a guard on a space station, not a soldier on a ship. The airlock thing is a good idea. If there's an evil AI doesn't that mean that any piece of random computer that's hooked up to the core become corrupt and try to kill you? Like for example, guard robots with laser guns or something like that. Also, you have to blow the station up and escape because the Bio-Rocket was so powerful it pushed the station back into earth's gravitational pull and will land and infect the earth if you don't. The demon was an experiment held on board the station to see how grizzly bears would react to zero-gravity, but when the AI got corrupted by a virus sent out by the evil force the experiment went horribly wrong and the bear got mutated. You may need to edit the sprite a little to make it look more like a bear, but that's my best idea about him.
As for the evil guy, He's from an alien planet just out of our solar system. After the people of earth started launching nuclear waste into space because we have no use for it, some landed on his planet, infecting the people. He waged war on the evil humans and uses their own waste against them by shooting a rocket containing the zombie virus thingamabob. It's a video game, right? who says it has to be scientifically accurate?
The mole is a robot created by the AI once corrupted.
Oh crap. I just realized that the AI wants to destroy the ship, right? because it's infected by the virus, right? And the virus was sent by the dark force. But that's a problem, because the evil guy wants the ship to remain intact and infected. So maybe the AI only wants the mole to destroy the electrical parts of the ship.
once again, feel free to point out any plot holes, random mistakes, and things you don't like.