Purple door Fortress of Glass

I cannot open this door. Clueless about where the key is or what method to use. Please help.

I'm not sure where you are. Are you in the Towers? If you are and there's a guard--what does he say? Leave quickly?

Yes, I am in the towers. The guard is Merlin. He urges me to use my mind to solve my problems and not insult him. I already have the queen’s ring if that helps.

If you've talked to Merlin, then the door is probably the one you need the Shock items for--The 'Shock Armor\' is in a vase along the north wall of the room that shocks you. The rest of the 'Shock Items' are in barrels in the Dungeon. There\'s a 'Shock Helm', \Shock Shield', 'Shock Armor' and 'Shock Leggings".

I have revisited the dungeon and had already emptied the barrels. I am missing the shock helm and shield. There is a door in the dungeon that I cannot open. Perhaps the others items are there. Can you help me with this door please?

They were in barrels there. Mrs. Phredd sells them though if you're desperate. She's in the Wizards' Lair.