Joey Operetta

Joey Operetta is an agent of Dio. His automatic colony stand, Murderdolls, attacks the party in the overworld throughout the journey. He is also fought numerous times as an optional boss throughout the game.

Personality
Joey is a businessman, but also a closet otaku who enjoys dress-up. Though his stand is usable on any doll, he chooses girl dolls primarily. He has no actual loyalty to Dio, only working for the payment. He initially goes to Japan to assassinate Joseph and Avdol while Kakyoin attacks Jotaro; however, as he commanded his stand to "kill all stand users that oppose Dio", they attack the player instead, as they are closer. He continues to pursue the group, but after goofing up his assassination attempts numerous times, he is deemed useless and eliminated by the Egypt 9 Glory Gods.

Singapore
On the 12th floor of the hotel, Joey appears surrounded by Murderdolls. Talk to him to initiate a battle. The dialogue in this battle differs for female protagonists, male protagonists with the Perverted trait, and depending on whether you chose to fight him before or after defeating Ebony Devil. In any case, after the battle, the doll Stands around Singapore will vanish. You will also get +1FP with whoever was in your party.

Calcutta
If you defeated Joey in Singapore and are male, there's a merchant who promises to show you cute young girls in the southwest corner of Calcutta. Accept his invitation, and you'll be taken to a cabaret, where you'll find yourself surrounded by Murderdoll EXs and soldiers. You can defeat Joey behind the counter to leave and gain FP with whoever is in your party. If Jotaro is your active party member, the dialogue will be slightly different.

Varanasi
If you defeated Joey in Singapore, there's a doctor near the hospital southwest of the hotel who'll offer to escort you to the clinic where Joseph is being examined. Choose to go with him to watch a cutscene followed by a battle with Joey, after which all the Murderdoll Lv. 5 enemies around town will disappear. (The Lv. 4s will remain.) You'll also recieve +1FP with whoever you beat them with.

Karachi
If you defeated Joey in Varanasi, you will be able to access Joey's warehouse in the alleyway with a zombie walking around in the shadows near some barrels in the the easternmost part of Karachi. Walking to the end of this alleyway and turning left will grant access to Joey's warehouse. Events that play in the top floor depend on your gender and your current party member. After the event, if you are female, you will gain 1 to 2 FP if you were with Jotaro or Joseph, 1 to 3 FP if you were with Kakyoin, and 1 to 3 FP if you were with Polnareff (if you are Chubby, you will only gain 1 FP with Polnareff).

If you don't interact with the treasure chests in Don Cherry's mansion and in Joey's warehouse, you'll be able to press a switch on the black suitcase on the top floor, which will open up a hidden door to the basement.

Fishing Village
If you defeated Joey in Varanasi, you can talk to the girl sitting at the bar, and you'll notice something strange about her style of speaking. Afterwards, you'll be forced into a final showdown with Joey in a desert outside town.

Trivia

 * According to Clayman, Joey can control anything as long as it’s doll. The figure body model of Murderdolls is not made from scratch, but is “an improvised wax figure of a corpse soaked in wax.” Level 3 and above Murderdolls are made of it. He mainly collects corpses in a popular suicide spot by using Murderdolls, but sometimes he "procures" them locally because there is a limit to the number of corpses he can collect in a suicide spot.
 * According to Clayman, Joey doesn't distinguish between dolls and humans. He thinks of people as if they were robots made of flesh or like NPCs in a game. He thinks at a level below the conscious mind that others are “philosophical zombies.” His mind was distorted and broken in this way because of the abuse and the strict upbringing by his parents.