Osiris

Osiris is a humanoid Stand; with large, muscular arms marked by lines of a vascular pattern; of a thick brow, and fingers capped by suckers. It is only revealed from the chest up; mist obscuring its possible lower half.

According to JOJOVELLER, its appearance is a rearranged African traditional picture, with mechanical parts.

In the colored manga, Osiris is portrayed as being purple with yellow eyes. In the anime, it is green with red eyes. In the OVA, it is portrayed as being being light green.

It doesn't show any personality and follows Daniel's instruction mindlessly.

Osiris represents the Egyptian God Osiris; related to prosperity and life after death.

Ability

Osiris is an Automatic Stand that completes Daniel J. D'Arby's gambling and cheating skills. More precisely, it is the cooperation of Daniel's gambling and Osiris' ability to steal souls on easy-to-reach conditions that make the pair so dangerous. Because of this, Daniel nearly defeated the entirety of the Joestar Group.

Soul Steal

Osiris has the ability to take the soul of anyone who loses against D'Arby be it in a bet or in a game^[1].

More specifically, it will act when the opponent "admits defeat in their heart", which is said to reduce their soul energy to near-zero. However, D'Arby needs his opponent to agree to gambling their soul^[2]. If the loser bets the soul of another person, Osiris can take it even if that person is not present or agrees with it^[3]. Cheating is allowed when gambling against D'Arby, who he himself considers perfectly acceptable, as long as you don't get caught^[2].

The souls are compressed by Osiris' fists and stored in a semblance of poker chips^[2], which D'Arby keeps as a collection. D'Arby is then free to gamble individual souls^[2] or even split a chips in several blank pieces to used in a game, with all of the parts being equal to one soul^[4]. If he recognizes defeat, the souls he's gambled are released^[5]. He can also release the souls at will if he wants^[5].

According to Daniel, if he dies, so does the people from whom he took the souls^[2].