The first time that we meet Joker, you wouldn't know who's team he's batting for. He's pretty observant and did gave some insights into Team Hokage's matches. He did save Menou from Team Uruha Oto's attack. You really wouldn't think that he's a part of the Uruha Jyuushinshu since he was just an observer. And like a Joker in a deck of cards, you wouldn't really know how he's playing. He's pretty mysterious and vague.
Like a joker or a jester, Joker doesn't take things seriously. He likes to kid and goof around, be silly, and even show off. In his battle with Jisho prior to joining the Jyuushinshu, Jisho did say that it seems that he isn't really taking their fight seriously. And so his full potential isn't really evident in his battles.
Joker is someone who really doesn't play by someone's rules. He may be part of the Jyuushinshu and is led by Kurei but he doesn't follow Kurei's orders and instead just do what he wants. When Kurei ordered Joker to kill Koganei, since Joker was intrigued by Koganei and wants to fight him in the tournament, he instead spared Koganei's life and also provoked Koganei in fighting him seriously. But eventhough Joker isn't one for orders, he is one of the most loyal to Kurei of the Jyuushinshu. Up until the final arc, when almost everyone was either dead or are now underlings to Mori, he was there, along with Neon and Raiha, beside Kurei fighting against Mori and his army.