To get the Mask of Truth You must sell four other masks.
The Guard at the death mountain trail wants a mask. go to the mask shop and buy the Keaton Mask. sell it to the man.
Sell the Skull mask to the Skull Kid in the Lost Woods.
Sell the Spoky Mask to the Young boy in the graveyard.
Sell the Bunny Hood to the marathon Runner. Go behind Lon Lon Ranch at night to find him.
Now you can get the Mask of Truth from the mask shop.
