A popular game with young people is babanuki (Old Maid), usually played with 4-5 people. For this game players use the entire deck plus one Joker. All the cards are passed out. To begin, all players try to make pairs with the cards in their hand. They can lay down all their matches. Play begins when the first player pulls a card randomly from the next players hand. If it matches one in his hand, he lays that pair down. If not, he keeps it. The next player picks a random card from the person next to him and tries to make a match. Play continues until, in the end, everyone has matched up all their cards except for one person. The person holding the Joker at the end of the game is the loser.
(source)

JOKER #1: SUDOU TATSUYA
Sudou Tatsuya is the son of the Foreign Affairs Minister, Sudou Tatsuzou. He hears voices (he's what, a denpa shounen?) and the voices drive him to do things. On the Other Side, he was merely an arsonist, but on this side, it seems that he was a killer as well. Ten years ago, when he was 18, he went on a killing spree that was investigated by Tatsuya and Katsuya's father. There was a coverup, and Mr. Suou got blackmailed while Sudou Tatsuya was institutionalized by his father.

So he spent ten years in the Morimoto Mental Institution on top of Mt. Katatsumuri, until I suppose Nyarlathotep visited him to awaken his memories of the Other Side. If you look at his cell, it's covered with drawings of a giant eye and butterflies - the black butterfly of Nyarlathotep? He also started remembering fractions of the Oracle that he had composed on the Other Side - the Oracle of Maiya. He apparently kept writing down what he could remember until he had the completed Oracle, which Maya reads on the walls of his cell.

On the other side, Sudou idolized Joker-sama, who had freed him from the asylum and had taken care of him. Perhaps Nyarlathotep suggested that if Sudou recreated the events of the Other Side, Jun would remember that he was Joker-sama, and he would again lead the Masquerade and take care of Sudou.

A rumor spread among the HS students that if you dialed your own number, the JOKER (there's a big difference in how they're written in the two games - ジョーカ様 vs. JOKER) would appear and kill the person you hated. This was known as the Joker Curse. Again, a clear parallel to the Joker Charm of Tsumi - but Jun wanted to make people's dreams come true, in his own weird way. Sudou doesn't have such lofty ideals; he probably just wants to lash out at those who hurt him (especially on the Other Side). Apparently the victims of the JOKER Curse looked like they had been torn apart by a wild animal - Sudou's Hellhound, I guess.

He awakens the persona-summoning power of "the witch" Maya, inadvertently awakening the abilities of her friend Ulala and the cop that was with her. Once this part of the past had been started, Maya fought in the clock tower, and eventually was lured back to the Air Museum where King Leo had been killed on the Other Side. This time Sudou also lured Kashihara Jun to the museum, hoping to awaken his memories as Kurosu Jun/Joker-sama. The flower that he offers to Jun is the flower Joker-sama had given him on the Other Side to give to Tatsuya as a message of revenge - that's why he expects it to jog Jun's memory and why Tatsuya tells Jun not to think too hard about it.

But again, Sudou's face is burned, Joker-sama turns on him to protect his friends, and he gets killed in the blimp. I don't know, I feel kind of sorry for him - but perhaps I'm thinking more of how he was on the Tsumi side, kind of pathetic and insane instead of evil and insane.

In the EX Dungeon, you have to give him three items to awaken his memory - read about that here.


JOKER TYPE #2: PEOPLE WHO USED THE JOKER CURSE
This is pretty self-explanatory. This includes Katayama Noriko, Serizawa Ulala, and Sugimoto Hiroki. All of them (except for Ulala) were collected by the Tien Tao Lien and taken to a laboratory where their kegare was extracted and put into collection tanks.


JOKER TYPE #3: JOKER == KEGARE

Now it seems that the Joker is merely the Shadow self, and the persona itself is the collective sins and fears of the people. Well, all right...

[ OTHER SIDE]