Assassin's Creed II/Sequence 9: Carnevale

You'll get a powerful new attachment for your hidden blade in this sequence, and the goal is to infiltrate a Carnevale party to get to Marco Barbarigo. When you learn of a competition for the Golden Mask, three of the four challenges will become available at the same time, and they can be completed in any order. Only when you've finished them will the last challenge be accessible.

Knowledge is power
You need to test out the new hidden blade attachment Leonardo made from the Codex page you brought him, so head south and hop over the wall to the garden behind it. Go out back to the dock to start pistol training. There are three target dummies, two on docks to your left and right and one up on a window ledge above the dock on the right. Pull out your pistol with the weapon selector wheel, then lock on to a target and hold the armed hand button until you've drawn a tight bead on your target. Release to fire. Take out all three targets, then head back to Leonardo's workshop. The pistol holds six shots, and when you run out you can buy more from a blacksmith for 175ƒ apiece.
 * Memory start: Knock on the door of Leonardo's workshop.
 * Reward: 2,000ƒ, Pistol, Carnevale mask, Assassination contracts unlocked

Damsels in distress
As soon as you're introduced to sister Teodora, a murderer will run through the house and you'll need to take him out. He runs away from you from girl to girl and slits their throats if you get too close. Head west to where he's holding his first hostage. Inch up to him until you can lock on, then use your recently learned pistol skill to take him out. It's best to do it the first chance you get, as later on there will be guards nearby and you'll have to escape or fight them when the memory concludes.
 * Memory start: Knock on the door to La Rosa della Virtù in the Dorsoduro district.
 * Reward: 3,000ƒ

Nun the wiser
Just follow sister Teodora and Antonio to the Squero di San Trovaso. When you get there you'll find out that to win a Golden Mask, which gets you into the Doge's party, you'll need to win a competition.
 * Memory start: Knock on the door to La Rosa della Virtù.
 * Reward: 3,000ƒ

Ribbon round-up
You need to obtain ribbons from the women around the area, supposedly by charming them. Ezio has other skills at his disposal, so you just need to walk around to each of the groups while holding the legs button to steal the ribbons from them. The groups are marked on the minimap with blue objective markers and the ladies don't put up a fight, making this the easiest challenge you'll need to compete for the Golden Mask. You need to collect 25 ribbons in four minutes and the ladies carry small, medium and large bundles of them. When you've got the ones inside the square, head out into the streets to find more groups of women.
 * Memory start: Talk to the man in the northeast corner of the Squero di San Trovaso.
 * Reward: 3,000ƒ

CTF
The goal of the game is to grab the flag and return it to your home base. If your opponent gets it, you'll need to chase him down and tackle him to get it back. Likewise, he'll be trying to do the same to you when you have the flag. You can get the flag back from the other guy by getting near him for a second or two, by tackling him or by punching him (since you'll meet the first requirement). You win when you've brought the flag back three times, and you desynchronize if your opponent does the same. You start out on top of a roof and the flag is down on the ground directly north of you. Your opponent is on his way from a rooftop to the west. If you want to let the other guy get the flag and cherrypick his base, just proceed due west and slightly north to another curtained stall on the farthest west building, right on the water.
 * Memory start: Talk to the man next to the Santa Maria Dei Carmini, northwest of the Squero di San Trovaso.
 * Reward: 3,000ƒ

There's no easy way to get down to the flag, at least not before the opponent gets to it. By this point you should have enough upgraded armor that you have a ton of health, and even more if you've been collecting Codex pages, but if you're a little low, grab some health vials before attempting repeated jumps down to the flag. From where you start the memory, sprint down the roof you start on toward the flag. Free run across the wooden balcony behind the side of the building in your way, then continue straight on directly at the Santa Maria Dei Carmini (the big white building with the gray roof). You'll jump off toward it, land on the very edge of the building below before falling to ground, which puts you just to the right of the flag and costs two health squares. Grab the flag and head directly back south through the archway to the next courtyard. As you're heading this way, avoid the opponent (he's pretty bad at getting the flag back from you), and you should see some crates on the left side of the next area with white sheets on them. Free run up them, which will take you to the roof via a series of protruding poles. Climb up one more level to your base and head into the white marker.

You can get away with this tactic twice before the game gets wise and the pursuit guard you're racing puts on his super speed. After the first two flags you capture, save yourself the trouble and just head to his base to nab the flag back there. Capture the flag for the third time and you've won the competition and are one step closer to the Golden Mask.

And they're off
If you've been doing the races side-missions, this memory will be very familiar to you. Simply run from white marker to white marker within the time limit. You have two minutes when the memory starts, and the first marker is right in front of you. From there, head left and go over a footbridge, running through two more markers in the process. You can't see the next one, but it's right around the corner, so stay at street level. You'll see the next marker ahead of you between two fire-breathers, at the start of a free run sequence marked by crates with a white sheet on them. Head up this way and follow the jumps and climbs along the side of the buildings until you make it to the platform with the next white marker.
 * Memory start: Talk to the man in front of the fast travel station by the Santa Maria Della Visitazione.
 * Reward: 3,000ƒ

Next, keep going straight and jump across the street via the wooden beams, then turn to your left and jump to the platform with the white marker. Keep going in this direction, which is a jump to swing around the corner. Follow the free run jumps and you'll hit the next marker when swinging to one of them. Continue along the side of the building until you get to the platform below the next marker. Climb up to the roof, passing through the marker on the way, then head to the other side of the roof and over the wires to the next marker. Next is another gap between buildings spanned by a wire, then up to the high part of the roof to hit the marker. From there head due west across the roofs to the marker in the distance. Keep going in the same direction to the end of the wooden beam jutting from the edge of the roof. Jump off the beam and dive into the canal beyond.

Swim to the steps and climb up into the next marker, then take off down the tunnel just beyond it. The next two markers are right in the middle of the street on your way to the last marker. For the last one, free run over the wall on the side of the ship and into the last white marker.

Cheaters never prosper
If you haven't already bought them, go purchase the Metal Cestus at a blacksmith, which are armored gloves that will greatly enhance your fists' lethality. In this fight weapons aren't allowed, and you'll desynchronize the memory if your opponent dies, which means poison can't be used either. You'll face a normal guard, a lightly armored guard and finally a heavily armored brute, but you can easily defeat them simply by wailing on them. Grabs will work on the first two if you're so inclined. If you're having any trouble with the brute, block and counter is a viable strategy as well.
 * Memory start: Talk to the man at the pier on the south side of the Squero di San Trovaso.
 * Reward: 3,000ƒ

After you've defeated the first three guys, Dante Moro, Marco Barbarigo's bodyguard, will enter the ring. Use the same strategy, as he's not much different, although you won't get as far with your counters on him. Silvio Barbarigo doesn't like that you've won all the competitions, and sends in four pursuit guards with weapons to finish you off. At this point you can go ahead and use weapons and kill your opponents. Treat it like any other fight against multiple enemies and take them all out to finish the memory.

Having a blast
Your job is to lift the Golden Mask from Dante without his notice. You start outside La Rosa della Virtù, and Dante is dancing in a side garden to the southeast of you. You'll need to steal the mask from him before he gets to the party or you'll lose him and the memory will desynchronize. When you head over to where he starts his walk, he'll come out onto the street followed by an entourage of fancy ladies. Get into a group of people until he passes you, then simply walk up behind him and steal from him. If he sees you, he'll pull out his axe and chase you, but you can just head to the party (or go back for another shot if you didn't steal the mask). When you get the mask, your objective will change to crashing the party and the memory wall blocking that area will disappear.
 * Memory start: Knock on the door to La Rosa della Virtù.
 * Reward:

Once you get to the party, head through one of the arches to the east, which is the only way not blocked by a memory wall. There you'll run into Teodora, who will inform you that Marco Barbarigo is on the boat and will address the crowd. When you join the party, Dante will show up and be looking for the person who stole his mask. He sends his guards out into the crowd to look for you, and you'll need to evade detection for one minute, after which Marco will come out make his speech. It's actually easier to not blend in with crowds here, because as soon as you do, a brute with a spear will approach to check the group out. You can just wander around, keeping in the center of the red dots on your minimap and shying away from any direction where you see an alert symbol starting to fill up, but the easiest method is to hide in the hay cart by the water in the southeast section of the area. You may have to stealth assassinate one of the brutes while his buddy isn't looking, but sometimes even that won't be necessary.

When he comes out to talk, Marco doesn't leave his ship, which means you will have difficulty trying for an up close approach. If you're spotted by any guard during this time, the memory will automatically desynchronize as Marco flees. Teodora suggests you use your pistol from a distance and time the shot with the fireworks so it goes unnoticed, however, this is really bad advice if you weren't planning on fighting all the guards in the area. If you want to use the pistol you can, after which jump into the water and swim away to escape. For a silent hit, walk close enough to Marco to lock on, then back up until you're in the middle of the area with no guards around and throw two knives into him. This will take him out and you'll stay incognito. After that you just need to get beyond the borders of the yellow area shown on your map, which will include swimming away, unless you take the rooftops to the south.

When you are outside the yellow perimeter, head to the new objective marker on your map, which will take you northwest back to La Rosa della Virtù. Bear in mind that during this time you will be completely notorious, so you'll still want to avoid running into any guards along the way.