The reason why these mobs were not in first page is obvious:
Undeads are very popular in other mods that add mobs, The undeads such as Grim Reaper, Lich, Necromancers... are very common around these mods.
Hydra was appeared at Twilight Forest mod, And it also has unique AI and spacial attack move.
Wendigo is appeared at Mowzie's mobs mod, Named Frostmaw, Both these are almost same design and ability (Strong health, freezes you to death)
Vampires and Werewolves are now already has there own mods...(See Vampirism mod and Howling moon mod)
Ghosts we're also very popular in other mods, But in my options, it can been tweak for more ability to make it unique (Such as no clipping like Vex, And can only been harmed with spacial weapons or spacial ways)
The only possable is for Automations, Automations can be small as ocelots or big as Iron golems, and like Iron golems, there're tough, tanky and powerful, And didn't affect with hunger, poison or wither (since there's kind of robots)....
No, they werent up there because we lost access to the account