Not sure if it's any better than the description you used, but one I came out with seemed decent by kind of forcing the AI to understand the goal. Some of them ended up looking weirdly looking like Koraidon, especially before I specified the ridges are "sharp red ridges" instead of just "sharp ridges." Might be able to fix that by specifying details about her neck and/or snout, but I didn't experiment that far.
Groudon is a massive, fat anthro lizard. The top half of her body is covered in red scales with black patterning between scales, while the bottom half of her is covered by a dark gray underbelly. She has white spikes running down the sides of her body, and both her fingers and toes are made of these white spikes. She has sharp red ridges extending above her snout and her short, wide tail. Her eyes are yellow and are surrounded by black patterning. Her belly and breasts are huge, and her gray boobs have red tipped nipples. Her hips, abdomen, and butt are very large.
Featuring some example pictures.
