The "Haunted Dimension" is dimension from the DS version of "Phineas and Ferb: Across the 2nd Dimension (video game)". It comes right after the Music Dimension.
The gang arrive here and look around. Phineas quickly remarks that they're not at their dimension, since he would have remembered the monsters.
After the battle with the Giant Skeleton, the gang get enough energy to go to the next dimension: the Toy Dimension.
The dimension has a haunted-theme to it, as the name implies. The sky is darkened and some fading in and out monsters are seen on the background.
- Giant Skeleton