From Bulbapedia, the community-driven Pokémon encyclopedia.
Litwick Mansion (Japanese: ヒトモシ屋敷 Hitomoshi Mansion) is an anime-exclusive building located along Route 4 in Unova. It made its appearance in Scare at the Litwick Mansion!.
Litwick Mansion was first discovered by Ash and his friends while trying to get out of the rain, while unbeknownst to them, the mansion had been discovered by Team Rocket first and was being used as a temporary base, due to it being abandoned and in a good state. However, the mansion was the home of four Litwick and a Lampent, who proceeded to try to scare Ash and his friends and drain Team Rocket's life force. The Litwick began to use Psychic to bring everyone closer to each other, where they lured them down to the mansion basement. Along the way, the Litwick abducted Axew, Yamask, Pikachu, and Meowth.
After the gang confronted the Litwick and their leader Lampent, the Ghost-type Pokémon opened a vortex to the Ghost World to try to suck Ash, Cilan, Iris and Team Rocket into it and began using Shadow Ball and Inferno to push them into it. However, everyone began to fight back with teamwork using Pikachu, Oshawott, Dwebble, Woobat and Yamask to save themselves and send the Litwick and Lampent into their own vortex. After defeating the Litwick and Lampent, they left, and when they got outside they saw that the mansion was ruined. Then, Team Rocket escaped from the mansion and it started raining again. Ash and his friends then went to get covered from the rain in a hollow tree stump.