The E3 trailer is one. Ezio is able to approach his target easily while most of the guards are taken out by unseen allies. As Ezio is faced with a dozen other guards, we see four other Assassins come out and stand next to him. The two sides then charge at each other, and end the trailer by clashing.
So is the trailer that essentially consists of the dev team showing you a bunch of awesome new ways to murder your friends in multiplayer mode.
No actually, most of the stuff in the trailer is impossible in multiplayer mode, single player on the other hand...
At the end of Sequence 5 Claudia's girls have stolen a chest full of loot from the Templars, but the Templars have tracked them back to the Rosa in Fiore. Ezio enters expecting a big epic fight...and finds his little sister Claudia standing over four dead guards with a knife in her hand. The respect and admiration in Ezio's voice also doubles as a Crowning Moment of Heartwarming.
Apparently this little sequence is crowning in so many ways to warrant it on Funny, Heartwarming and Awesome.
After Cesare murders Rodrigo and flees to retrieve the Apple, Ezio still stops to close Rodrigo's eyes and utter yet another "Requiescat in Pace." It just shows how far beyond the conflict Ezio's gotten when he shows such respect to one of his worst enemies.
Ezio using the Apple to make Cesare's Papal Guards kill each other.
The Mercenary arena battles, it really shows how competent Ezio is and how widely he is respected. When he is shirtless, surrounded by mercenaries half his age, twice size and outnumbered 4 to 1 what is the challenge? to survive? to take at least one of them out? to win? No. The challenge is to see if he can do it in under 35 seconds.
To add to the awesomeness of this, the "full sync" challenges are implied to have actually happened the first time around. So yeah, He knocked out four men, all of whom closer to their prime than he, in under 35 seconds flat.
The first Leonardo's machines mission. Riding a cannon which you stole from the Borgia's army through the countryside, with soldiers on horseback on your tail whilst Ezio fires the cannon at them as he rides back to Roma? HOW CAN THAT NOT BE AWESOME.
Pretty much every one of Leonardo's machine missions, but one in particular made this troper giddy. You get to use LEONARDO'S TANK to kill scores of soldiers, cannon emplacements and TWO other tanks. Best mission of the whole game.
Even acknowledged in-universe as awesome. Right before Ezio destroys the tank he says he wishes he could keep it instead since it was just that awesome and the player probably agrees.
Made even more awesome by the implications of doing it at full sync, in which you have to avoid being hit at all'. This means that the actual Ezio did all of this without getting hit once.''
The flying machine mission, in light of the second game. In that one you needed fires set around the city in order to provide the glider with lift when it started to lose altitude. This new one however can launch fireballs down on your enemies...and the fires provide the necessary lift! So in the process of turning his invention into a machine of death, Leonardo also made its flight self-sustainable...via the exact same "unforgivable" act of making it a weapon in the first place. Only da Vinci could turn Insane Troll Logic into a moment of awesome.
One of Ezio's last lines before he kills Cesare
Ezio: (sounding a lot angrier than usual) ''"Che nessuno ricordi il tuo nome. (May no one remember your name.)"
So the studio producing The Borgias is run by Templars?
No because the Templars found the Borgia reign to be shameful to their organization so The Borgias is probably made by the Assassins.
The DLC, in which Leonardo snarks at the people who have him tied up and at their mercy and keep beating him up for information.
Monk: "Where is the entrance?"
Leonardo: "Why? Do you not know?"
Monk: "How could I?"
Leonardo: "You seem to know mankind's wants and needs; I assumed discovering the location of a mere hidden entrance would be an easy feat."
Monk: "...Why, you.... WHERE IS IT?
Hearing the vigilantes taunting the guards about the various ways they will die at your hands. Bonus points for proving the vigilantes right mere seconds later.
The random two Assassin recruits who each throw a knife at Pietro's bounds on the crucifix. Neither of them even waited for him to hit the ground before they turned around to fight off some guards for Ezio, they were just that confident in their aim.
I got one in the where Ezio wields the piece of Eden. I decided to use my flags not to wipe out all of the enemies on the battlefield (expecting additional waves) but to summon all of my assassin recruits. To my surprise, they (along with Machiavelli, Claudia, and La Volpe) were able to take on all of the Borgia forces, to the point that Ezio simply stood there holding the Piece of Eden WITHOUT BEING ATTACKED.
The Malfatto mission requires that you kill him using your recruits for full synch. Last time I did it, one of my Assassins popped out of a bale of hay and stabbed him point blank. They are EVERYWHERE.
Really, any time one of your little recruits goes above and beyond the call of duty (and it's usually hilarious, too). Signaling one recruit to eliminate one inconvenient guard only to have him or her take out the guard, his four friends over in the corner, the target, and the target's dog is not only awesome (and a testament to Ezio's training aptitude) but hilarious.
Speaking of the recruits, any time one of them reaches max level and Ezio initiates them into the order. The initiation ceremony is pretty cool, and at the end of it, the Assassin will now sport a Badass Long Robe much like Ezio's.