Carnevale

The Carnevale is an annual event held in Venice, Italy. It is essentially a carnival unique to Venice where people wear masks.

Ezio obtained a mask and had his Plain Cape embroidered during this event, in order to remain anonymous. It is during this event that Ezio retrieved the Golden Mask to gain entrance to Marco Barbarigo's personal party, in order to assassinate him.

Despite being featured in the trailer, Carnevale itself has no major role beyond the assassination of Marco Barbarigo.

Attire
During the Carnevale, by wearing a Carnevale mask and cape given to him by Leonardo da Vinci, Ezio was able to avoid suspicion from the guards.

After participating in and winning the Carnevale's games, Ezio earned his prize, the Golden Mask. However, Silvio Barbarigo secretly bribed the Carnevale's Master of Ceremonies to give the Golden Mask to Dante Moro instead. Ezio then pickpocketed the Golden Mask from Dante and wore it, replacing his plain mask and granting himself access to Marco Barbarigo's party.

Trivia

 * Even after the events of Carnevale, the citizens will continue to celebrate it for the remainder of the game, albeit without fireworks, in the district of Dorsoduro.
 * You cannot change outfits during Carnevale.