Wait, this thread is almost 3 years old and Nightmare still don't have a gargoyle? XD
C'mon now, a creepyass mansion like that must have a stoned bat hanging around somewhere.
But other then that... I think almost all well known creatures of the night are present. We got zombies, skeletons, witches, vampires, demons, dolls, ghosts, werewolves, dragons, Cthulu, scarecrows, clowns etc. etc. Aside from the gargoyle I don't think there's any 'must-have' left.
I better go 'n play a Castlevania to see if I forgot any ;)
Hairy Jack, Fear Liath, Black Dog, Afanc, Jack Frost, Jack o' Lantern, Ogopogo, Nessie, Poltergeist, Gashadokuro, Utai-Gaikotsu, Itsumade, Jueyuan, Kaiming Shou, Gu Huo Niao, Zhu Tun She, Shan Xiao, Gandarewa, Pocong, Rangda, Draugr, Will-o-Wisp, etc.
A lot really, a lot.
They need that Japanese legend involving that girl with a slit-open mouth. Words can't describe it accurately, but this story gave me nightmares as a child, and when I saw the film adaptation
Blood thirsty unicorns,ogres,shinigami, and lycans should be near the top of this list.
Anything from the Stephen King books would be huge also.