Fast & loose concept sketches.
I model in Sculptris, which I find particularly intuitive. While I model, I look at pictures of actual slugs and am reminded of anatomical details not present in my concepts. I add those, and I will later realise I want the eyes to be bigger.
I imported my model to meshmixer to scale it and give it a perfectly flat base.
Then I import to Cura to slice the model for 3D printing, with support structures.
Primed for painting.
Comparison with a 25mm miniature from a Dungeons and Dragons game.
I model the second slug creature, with the teeth. I know real slugs don't have mouths like this, but it sure looks nice.
This time I know that bloodshot eyes won't show up on a model only millimetres big, but the bumps and veins will.
Again, I paint the model to best present it.