Ancalagon
Dusty Dragon
Nightmare...imagine having to put together a level 15, 3.X character, right at the table because you opened the wrong door... All the skill points and feat chains shenanigans that existed... No time to go for Prestige Class amirite?
You know what I just realized? You could make a level 15 fighter (champion or brute) in... 3-4 minutes though in 5e? Doable. Heck, if you wanted something a little bit more complex, you could make a battle master or a thief or assassin in less than 10 minutes. And it wouldn't be a great or inspired character, but it would be perfectly adequate. In PF, if you don't already have a build in your back pocket... forget about it. In 5e, auto-pilot made characters are good enough. So you could play it a bit more dangerous if you wanted...