You need to have a Troupple Chalice to meet him. You can buy one from somebody at the Armor Outpost. I can't remember the name of that person who has the chalice, but I do know that she wears the same outfit as Troupple Acolyte.

For this task, you must hold onto 50 Cipher Coins and then enter the Armor Outpost. Pay those coins to gain the catapult and activate it. You will then need to fight off a number of minor knights before gaining full access to the Armor Outpost. The Troupple Accolyte will be waiting for you near the exit of the outpost. Now you can FINALLY gain access to five of the six magical cloaks.

steal the armor outpost