[From the forums -stabguy]
Here is my fastest blitz for Silvio and Dante:
Setup Dante: I run up to Dante and engage him in combat. Then I climb into La Arsenale, making sure Dante is still after me. I run far into La Arsenale so that the door and walls at the entrance will not be modeled in the game. This gives Dante a chance to get though. Go back, and if Dante is there grab him. Do not engage him in combat or he will fight you.
I place Dante at the edge of the docks and knock him off with a throwing knife. His drowning will start the scene, and if you are currently in water you won't get teleported to the checkpoint during the scene. The best time to climb up the docks is during the second scene. Where you move depends which way the camera is facing, so the best time to start moving is right after Silvio says "they're going to leave without us" . Move forward left until the screen turns white to grab onto the docks, then move forward to up climb the docks. Now comes the blitz. The two targets are far apart when they start running, but they get close enough for a double air assassination when they get in place. A few times I've gotten it a bit faster, but only gotten Sylvio since he's so close to the wall-running platform. Theoretically it might be possible to get a faster blitz, though.
This is not a "variety pack" video on the assassination of Dante Moro. Rather, it demonstrates how to use a variety of exploits to kill Dante practically every time he appears in the story during Sequences 8, 9 and 10. Each time he manages to rise from the dead.
This is very similar to a previous video:
Dante and Silvio start running from you once you cross the threshold to l'Arsenale. So don't. Go over the walls instead, and you'll find your targets as (mostly) unresponsive puppets.
The goal is to shoot Dante Moro and Silvio Barbarigo from as far away as possible. This mission relies on the unusual mechanics of the hidden gun. You need to be within 15 m to lock onto a target. Once locked on, you can maintain that lock if you remain within 30 m. If you start to aim the gun at your target while you are locked on, you will be able to maintain your aim. The shot will hit its mark as long as nothing obstructs the path of the bullet, regardless of how far the target travels from you.
If you don't enter l'Arsenale, you will stay Anonymous and the targets won't move past their first waypoint. This is the perfect opportunity to kill them with throwing knives. They will be too far away to lock onto, so you'll have to aim "manually." Throwing knives travel in the direction of your last horizontal movement. Walk in the direction you would like to aim, and look over Ezio's head to fine tune your aim.