To do his iconic open maw with mandibles use these tags:

split jaw, open mouth, mandibles

It also helps if you add my Reaper Lora somewhere between 0.2-0.4 weight. You don't have to add any other tags if you're already using ones above.

It tends to do random styles unless instructed otherwise - it switches between flat color 2d art to photorealistic/3d. Tag in the style you want or use a style Lora.

There were many photorealistic images in the dataset, so if you don't want that, I'd suggest you put "3d, realistic, photorealistic," in the negative prompt.