Are there any Xanathar Strategies for Skullport
As a general rule, you should be looking to take more actions that give you corruption than the other players. For all players, these actions give more resources than other actions in exchange for an end-game penalty. For The Xanathar, this end-game penalty is less than it is for other players. If you end the game with no corruption tokens with The Xanathar, then you haven't taken any advantage of his strategy, and you have just played the way you would have with any other Lord.

If you end the game with 10 corruption tokens, and no one else has any, then you will get -40 from the penalty, and 40 from The Xanathar's bonus. It is NOT accurate in this case to say that you got no bonus from The Xanathar. Rather, you got a 40 point bonus. The -40 that you got is theoretically offset by the extra-powerful actions and quests that you had throughout the game.

While other players will be taking those extra powerful actions and quests sometimes, they will also be spending other actions to get rid of corruption. Either way, this means that the player who ends with the most corruption should have gotten more out of their actions throughout the game than other players.

This doesn't mean that you should go crazy with taking corruption. If you have 19 corruption tiles, for -7 each, then the bonus isn't going to be enough to save you from that.

Finally, keep in mind that The Xanathar is more difficult to play than the other Lords, and it very well may be weaker in general.

Here are a few threads where this is discussed in depth:

How to win with the Xanathar

Xanathar, Halaster, Sangalor: New lord cards broken?

The Xanathar