O Haiku #atozchallenge

Yes, they’re big and mean,
Standard fairy-tale monsters –
But Shrek had a heart.

Welcome to today’s haiku puzzle for the A to Z Blogging Challenge. Your job is to figure out the word relating to science fiction or fantasy that starts with O, and that is suggested by today’s haiku. This one’s not the name of an individual, but a general term for a type of creature. Got it? Tell us in the comments.