From Sonic Retro
The Skeleton Dog is one of the rare animals found in Sonic Adventure 2, either either in the third Chao container or hidden somewhere difficult in the stage, with the sole exception of Pumpkin Hill, where it's treated as normal and therefore found in the second Chao container and hidden in the level. Its category is ghost and allows animal features from Chao to be removed and hats to be worn.
|Knuckles||Pumpkin Hill, Death Chamber|
|Dark||Eggman||Sand Ocean, Lost Colony|