Assassinate Robert de Sable

This is one of the hardest assassination missions in the game. You can spend a couple hours doing this and still come up short. There will be wave after wave of foes before you finally reach the real Robert de Sable. Unfortunately, there is no way around it. You must fight, and you must win.

I’ve read one suggestion online that says:

The easiest thing to do is get out the hidden blade and counter one of them.
Although it is difficult and the timing is strict, once you nail one of them at least one of the other guards should back away in fear, letting you simply jump onto him with the wrist blade.

For every kill one of the guards should react like this, so you can easily combo most of the guards down using this little tactic…

I’ve read another that recommends you fight, then just keep running in circles until your health regenerates.

If you’re still having trouble, check out this video below. It may give you a better idea of how to accomplish this mission.