I think that, without the Oni Link mask, you had to use the "Song of Healing" Masks, Boomerang fins in first form to stun, then run up to Majora with the Great Fairy's Sword. Second, use Goron form to chase him around (Majora was the most spastic thing I had ever seen). But the Deku mask is quite useless, because in the final form, you shoot the guy with arrows, not bubbles!