Garo's Mask: Have a possible speak with dead effect?
Captain's Hat: Gain the ability to rebuke undead. Maybe with an effective cleric level equal to around half your meldshaper level. Essentia investment to raise the effective level/some relevant roll.

Kafei's Mask should have something to do with Gather Information, since that was its primary (and only) use in game.

You should add Odalwa's, Goht's, Twinmold's, and fishie-thing's remains. Effects on those I'm not sure. And Majora's Mask itself, if you feel like doing something Epic. Have it require one of the epic feats, maybe make it Totemist Soul or Soulborn Heart/Soul chakra. No idea what that would do though.