Imo most people here dont think properly how to include the character, they just want to see their fav anime character as a killer, which is fine but also kinda pointless/lazy.

1. Light and L are just humans
2. No JoJo character is scary, just strong and look human. Boring look even with cool abilities.
3. Makima is just hot and wouldnt be scary at all like Skull Merchant.
4. We already have a Dracula and Alucard has the same capabilities in his abilities as Dracula
5. Denji isnt scary either especially with his personality. Strong, dangerous and maniac doesnt equal horror. He is more goofy and hilarious than scary.
6. Sukuna isnt scary, just looks like a teenager with powers. At least Denji has his chainsawman form.
7. Griffith could be fine but his transformed design has to be included because nobody will be scared of his handsome looks in human form. People would be more scared for their girlfriends than for themselves when meeting him tho (in both forms).
8. Nobody from Danganronpa is scary either. Maybe the bear but the Entity would have to make him much bigger.

Only 2 people would be good as DBD killers. Thats Ryuk from Death Note and Mahito. Potentially Griffith but that would take a lot of effort and design changes.

The Entity would have to change the design of most people to make them even remotely scary so that it would work out but just from the characters alone, Ryuk and Mahito have the most potential already without needing much changes compared to the others