A Short Theory About the Little Tree at the Beginning of Majora's Mask
I don't know if this theory is well known or not, lets see.
As you probably know the sad looking tree at the beginning of Zelda: Majora's Mask is/was the son of that Deku butler at the palace. What you maybe don't know is, why his son is dead.
I thought about it for a while and now im pretty sure I know the answer:
Every character in the game that left one of these "transform masks" died, so theoretically it is not possible to get one of these masks without "killing" the particular being. I think Horror Kid killed the Deku for the mask and then it used this mask to transform Link. And at the end, when the spell is lifted, Link recieves the mask of that Deku. This would also explain why the butler says, that Link looks very similar to his son while Link is wearing the mask.
I don't know if this theory is already known or not. Maybe I'm just a late starter.