Stronghold Crusader 2 willl be welcoming back the Assassin. The Assassin hasn't been seen since Stronghold 2, but he will be unleashing his particular mix of high damage, stealth, and presumably, climbing into the fray once more in the upcoming sequel.
The concept art is all we have so far, but we do know a few details. As before, your assassins can be trained up to become an important line of infiltration. You can use them as bodyguards or even slip them into a castle and surround the ruling enemy Lord with your blades before he even knows what's going on.