If you need the "Magical Masque" and the "MP Mambo", then you need to acquire two key items: Magical Dances, Vol. I and Magical Dances, Vol. II.

This is how to get them... (SPOILER)Volume I is obtained by defeating the boss enemies inside the Den of Woe at Mushroom Rock. Volume II is obtained by defeating the Experiment machine at Djose Temple during Chapter 5.

And I'm not quite sure about that whole Blue Bullet thing... Err... o_o;