User blog comment:ClericofMadness/Big Ol' To-Do List/@comment-4315974-20110831050857/@comment-3131641-20110831055139

This is my rule of thumb for telling the difference:

Cryptids - Monsters/rare animals you see in legends like Bigfoot, Loch Ness Monster, etc.

Monsters - Non-legendary, non-demonic creatures. The key thing here is that you get a clear description of what the thing looks like. Zombies are usually included in here, too.

Beings - Vague, mysterious things. You know something's there, but you never get a good glimpse of it, and you don't really know what it is.