I think part of the reason this one was so difficult for me anyway was because I had really never drawn horses before. In order to try to get a basic understanding of the skull and overall proportions of the head I needed to do some sketching beforehand, a few of them shown below.
After I'd had a basic idea of what shapes I needed for a recognizable horse creature, it was time to move into Photoshop and see what kind of weird concoctions I could come up with.
Just trying to go in as many directions as possible. The leftmost one is a little too sci fi, but I was going for something slick and slimy that moves about freely in water and air alike.
The second design began with a pose of a horse I had seen before starting--the silhouette was strong and really captured the recognizable shape so I wanted to emulate that. Slightly less corporeal and more of a ghoul actually. The hand... tail...thing was something that came forth as I was working on it, I was thinking of how it would attack the player and drag them beneath the water.
Trying to return to emphasizing the aquatic aspect of the enemy in the 3rd design with cooler tones. I figured tendrils would be useful for latching onto the player. I think ultimately it's still too sci-fi and not quite in line with the look of the rest of the game though.
The final design was a result of focusing on the shape of the horse's skull, I thought there were some pretty interesting shapes to use there. The orb in the middle was inspired by cuttlefish eyes, just trying out ideas for a weak point. Without any limbs though, I don't think it has much of a chance of dragging the player anywhere.
If you've been reading all of these, much appreciated and keep in mind these were the first steps. Come time to start creating actual enemies we'll likely take the best parts from various ideas and put them together and revise things along the way. Hopefully I'll have more to show for the game as progress continues in the future, so keep an eye out.