Dark Boo

Dark Boos are purple-colored Boos that appear in Paper Mario: The Thousand-Year Door, Super Paper Mario and Mario & Luigi: Partners in Time.

Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Dark Boos may be found only in the hidden spot of the Poshley Sanctum, and also in the Pit of 100 Trials on levels 51-59. Dark Boos have the same moves as their white counterparts, although they have more HP and attack power.

Super Paper Mario
In Super Paper Mario, Dark Boos can be found in Underwhere Road and in a few rooms of the Flipside Pit of 100 Trials. Here, they hide in 3-D, waiting for the player to walk by. Then, they flip to 2-D and sneak attack them. While in 3D, they act just like regular Boos, turning intangible when looked at and chasing the player when not. Shadowy versions of Dark Boos, called Dark Dark Boos, can be found in the Flopside Pit of 100 Trials.

Mario & Luigi: Partners in Time
Dark Boos reappear in Mario & Luigi: Partners in Time in the Gritzy Caves area, once again stronger than a normal Boo. A Dark Boo's only attack has it appear behind a brother and ram him, similar to their regular counterparts, albeit much faster. If it opens up its right eye, the attack is aimed at Mario. If it opens up its left eye, the attack is aimed at Luigi. If one of the Mario Bros. is attacked, the Dark Boo steals either a normal Item or a Bros. Item and will flee with the item on the next turn if not defeated quickly. They are usually encountered in large groups, rarely appearing alongside other enemies. Dark Boos are resilient to Bro Flowers, Ice Flowers and Mix Flowers. Unlike the ones in the Paper Mario series, Dark Boos lack yellow eyes and the blue mouth/tongue. Their Japanese name implies that they are shyer than the normal Boos, and, thus, may not be the same enemy.

Trivia
This is the only enemy that has appeared in both the Paper Mario series and the Mario & Luigi series, but not in the 'main' series.