I was originally leaning towards 10-12 creatures for the book. After giving it some thought, I decided to go with 6 creatures.
Here is the lineup I currently have for the book:
The Eye of Phugg
The Ghost of Hollis Whateley
The Gingerdead Man
In addition, there will be in character pieces from Xavier Stone, occult investigator. A character sheet will be included for him as well.
At this time, the Barghest, Dream Reaver and Ghost of Hollis Whateley are done. I'm saving the Eye of Phugg for last, as I'm trying to figure out a good way of representing the fact that it causes insanity when you see it (as befits encountering something Mythos like)
I'm pretty pleased with what I've come up with so far; I didn't think I'd suddenly be inspired to write a short supplement of horror themed creatures for a Super Hero game, but hey, it's happening!