I thought of more ideas for the plot. Is it okay with you guys if the HMS is actually a villan, somehow linked to majora's spirit? The evil that left the mask at the end of the game went into skull kid [as the poisonous aura], so the HMS is trying to extract it for an unknown purpose. Does that sound like it will work? Link must defeat the HMS in the end, the mask and its power is forever destroyed [like in the Lord of the Rings] Solro's antidote would be a temporary fix.
Btw, in case anyone was wondering, what I say about the HMS in the roleplay is just for the RP we are having, I don't actually think he's evil in pure Zelda canon.