From the Super Mario Wiki
Spooktastic World is the second world in Wario World. The area is located inside a manor portal from Treasure Square. It contains a small castle, from where Wario has access to the haunted house known as Horror Manor, and next to it there is a circus that works as an entrance to Wonky Circus.
The world itself has an evening setting, complete with dried leaf-less tress and sharp end fences. The boss fought here is the Dual Dragon.