What fictional character/item is impossible to make in DnD?

I got into discussion with a friend who knows way more about dnd than me about what fictional characters or items are possible to make in DnD. It pretty much ended with me trying to guess what is impossible in DnD. So far everything i came up with Chainsaw man, Evangelion units, AM, scp 294. And a few others, are there even characters or items that cant work under the normal DnD rules?