--Why these?
Disease: Well, let's face it. I love playing with immunity systems and the biological sciences. I mean, there are few things resistant to this embodiment, but really?
This guy's just the plague that makes everyone sick. I'd make this one a rather unhappy god. Huehuehue.
Trickster: We all need a laugh. I mean, it could be omniscient at time, like Zak's character, announcing about the forum and look like a total nutcase. S/he'd prolly would screw about with mortals (Especially Apr1

) and do ridiculous things like change fire blasts into flower petal beams, change someone's gender temporarily, or even "switch" the person into another person they haaate(Heart swap like manaphy or like the fortune cookie thing from Freaky Friday). S/he's a dick, sure. But a funny one.
Imagination: A true neutral that exists in everyone's mind. Imagination goes with Thought. Thought would be of one's own conscious. And Imagination could be parallel to Insanity, but at the same time is couldn't be. Same for Creation. It can be creation, but it can't at the same time. S/he's everywhere. lol