Boorios are Boos that resemble Boo Mario from Super Mario Galaxy, they bahave the same way as Boos.
In A Koopa's Revenge
Boorios do not appear in A Koopa's Revenge.
In A Koopa's Revenge 2
Boorios appear in this game, behaving like a Boo. However, they only appear in House of Deception. About halfway through the level, there is a Mega-sized Boorio about the size of a Boohemoth. If Koopa has the ghost powerup, they won't harm the player like other Ghost enemies.