It is a strange process that I did just for fun and it heavily relies on making happy accidents.
It all started from a quick abstract thumbnail that I did in photoshop just using the lasso tool , filling up a randomly created selection and then draw on top features that made it look more like a creature than a random blob. Once that was done I jumped in 3dsmax, mapped this thumbnail onto a simple 3d plane and of this plane I cut the different parts of the creature and made them 3dimensional. You can see that the 3d model is really rough.
Why doing this? Well first of all I really like to experiment in my free time, so that was one of the reasons, but second and most important is that once the thumbnail is in 3d I could actually twist it, bend it, make different variations and poses out of it for free and in no time. For example just by playing with a symmetry modifier and rotating it in different angles you could come up with many unexpected variations.
The slide below shows how two of the variations sparked up my imagination and I ended up with two quick sketches of possible creature designs.Nothing weird here (apart from the badly composed slide), just regular sketching.
And this one made its way to a more refined sketch later on.
I've played with this weird process earlier, you can see another example here (the bottom of the post).