If it's like Tri, masks don't determine which stats he buffs, dances do.
In Tri, Cha-Cha had 4 selectable dances of which you could equip two to him. The combination of dances determined which 4 buffing abilities he had. Masks instead affect things like Cha-Cha's stats (raising or lowering attack/defense/HP etc.) which usually also providing him a secondary effect. For example: The Fluffy Mask would make it where Cha-Cha wouldn't attack a monster, and instead focus on gathering or dancing, which also giving you the ability to see a monster on the map by calling to him with the signal (pressing Start in the menu)
Sorry I didn't really answer your question. But it's not masks that determine what stats he buffs assuming the system is the same as Tri.
Check this out for info on what he did in Tri: http://monsterhunter.wikia.com/wiki/MH3:_Cha-Cha_Guide