Just returned from that crusie and they do have a masquerade party as the ship is leaving Venice,you can by them anywher,shop around if you can because depending on what you want they can get pricey.
The ship and activities are fine but don't expect the same party atmosphere you would find on a Caribbean cruise, remember I would say that 90% of the guests are from Europe so there is a more laid back atmosphere, the ports of call are great and the tours are fine,we did them all thru Carnival,if you have any specific questions let me know.One thing I can tell you is no matter what tour you take,aside from a drive by tour,you will do plenty of walking.
Al