Well, to draw Cedric Diggory, focus on his facial expressions and the style of his clothing. It's important to get the proportions right. Start with light strokes and build up the shading for a more realistic look.
One cool idea is a cake with a 3D cartoon car coming out of a garage. Another option could be a cake decorated with car stickers and toy cars. Boys would surely love these creative designs.
'One-Punch Man' can also be considered. While not strictly about fitness, it features heroes with extraordinary physical capabilities and their training regimens. 'Baki' is another option that emphasizes on intense martial arts training and physical development.
Old Batman comic covers tended to have a classic, comic book style. They might feature Batman's cape flowing dramatically, or a cityscape in the background to set the scene. The use of shading and highlights was common to add depth and mood.
It can provide a thrilling and mysterious experience. The puzzles add an element of challenge, while the dark theme creates a sense of suspense and intrigue.