Sin Collector not unlocking

[Rubby]

I've been tearing my hair out over this achievement since it's the last one I need. I've had all the entries in my bestiary for a couple months now, but I still haven't unlocked the achievement. I even went through today and spawned every possible enemy with the debug console, but still nothing. Is anyone else having this problem? Or does anyone know how to get this fixed? I honestly don't know if it's a bug or not.

[CheddarExuberant]

It's a bug, though most of the time it appears earlier than it's supposed to rather than later.

For now, all you can do is just keep playing like normal, and at some point it should pop up.

[LSDBunny]

Try fighting Delirium a couple of times. Appearently some of his transformations will be counted as entries even tho they don't have their own entry in the bestiary. At least I'm assuming that's what is the matter, since many, including myself, got the achievement before completing the bestiary, some of which, again including me, got it during a Delirium fight.