The Hidden Blade Assassin's Creed in Depth

http://www.youtube.com/watch?v=WdgEnXLMQN0

Anonymous Blitz
Move quickly between pillars so that guards cannot see you continuously. This buys you a few precious moments to approach the Baron for the kill.

Mysterious Death
The goal is to poison the target by hidden blade without being seen at all (no yellow bars), and without killing anyone other than the target. Ordinarily, "mysterious death" missions also include an escape, but this mission ends with success the instant the target is injected with poison, regardless of whether it is done by the hidden blade or a dart. There is no opportunity to escape due to the scripting of the mission.

0:57 Look down to see when the first guard turns around.
1:15 Jump past the second guard when he walks by. He will turn around again in just a moment.
1:17 Immediately drop over the ledge so he doesn't see you.
1:18 Immediately drop to the ground and poison the target before he has a chance to find you.

Spear from the Roof
The 4 Seekers just outside the gate will provide the spear(s). The goal is to get the spear to the rooftop for the assassination. This would not have been possible in AC2 because you can't carry spears as you climb. You still can't carry spears while climbing in Brotherhood, but you can throw them to the roof by aiming at a guard there.

2:50 The poison dart keeps the guard from spotting you, and his delayed death buys you time (other guards won't come looking for you).
3:30 You can charge up your throw while you wait.
3:48 Lock on and throw when the guard appears. Climb up and laugh hysterically at how far he was knocked back.

Heavy Weapon from the Roof
If you buy a heavy weapon sheath, you can carry a throwable heavy weapon with you as you climb.

Free Pantasilea
The goal is to free the prisoner without killing the target.
5:45 Use coins to distract the target so that he stops pacing around and remains facing the wrong way.
5:59 Now it's safe to grab Pantasilea and move her out of harms way.
6:25 Her hands stay tied unless you injure her.
6:38 Even when she is rescued, you can't progress the memory without killing the target. And you still have to stay Anonymous, otherwise the game ends in failure (with the Baron shooting the floor).

There is no floor
This is a new variant of "there is no spoon:"
http://www.thehiddenblade.com/dante-moro-and-silvio-barbarigo-assassinat...
In this mission, if you place the target under part of the structure and then run away far enough, the floor on which he stands is no longer modeled in the game. Use the smoke bomb to avoid detection as you grab and throw him under the archway. When you are far enough away, he falls to the depths of hell and dies. I suspect this trick can be used in other missions, too, including those of AC2.

Pay special attention to the arrow next to the minimap distance meter. At 7:54, the direction suddenly reverses from pointing up to pointing down.