I have been through the game before without the mask, but now i wonder what happens when i trade all my masks away, do i get them back? What happens if i want to go back and fight Twinmold, will i have the Giants Mask? Or if i want to go into the Milk Bar, will i have that mask? And what about the 3 transformation masks?
How it works is this. Each of the Giant's masks will want to play hide and seek with you. When you play with them you give them a few masks. You do not get any of these back untill you fight MM. By the time you play with all four of them, and talk to MM, you will not have any masks left, so MM gives you the FD mask, and you start the fight. When you go back and load your game starting from DotFD, you will have all your masks back, as well as the FD mask.