When the witcher first meets the ghost, the latter exclaims "Geralt of Rivia himself... you're renowned in the realm of the dead." It seems our hero's reputation knows no bounds.
If Geralt chose Triss to be Alvin's guardian in Chapter III, then he has to rescue Alvin from the Gambling Ghost, either through a fight or by beating him at a game of dice. If he does not kill the wraith to save Alvin, he has the choice to either let him live and keep him as a poker opponent, or send him to the great beyond.
- Killing the Gambling Ghost nets Geralt 200 in addition to the XP.
- If you left Alvin with Triss in Chapter III, the Ghost will not appear above his skeleton until you advance the Alvin quest to the point after you are told to give him the amulet.