Hi!
Interesting design.
Try looking at some games you like, and try to study how they represent details on the sprite. The handheld castlevania games occupy a nice realm of semi-realistic and gritty. They have a lot of monsters, so it may be a good place to start.
Come back with something to show, and we'll gladly help you. Unfortunately, there's not much anyone can do for you until you show some pixel art, we have no way to see where you're at.
As with any new artistic endeavor, it's best to just just take a dive, and not have any apprehension or fear about the outcome.