One of the games you can play is to make a scavenger hunt out of the whole evening and offer prizes for the people that get the most questions answered correctly. As each person enters you assign them all a number and give them small tags that they need to wear somewhere on their costume. Make the signs big enough to see but not so big that they ruin the look of the guest’ costumes. Each person is given a piece of paper and told to write down their guess for who each costumed guest is based on their number. If your masquerade ball has a rather large guest list then this may not be a practical game to play but there are variations you could play if the guest list is long. If you have a lot of guests then you pre-arrange with a certain number of guests to have them wear numbers. Of course this information needs to be a well kept secret for the game to work. At the end of the evening the one of the guests that is not wearing a number that guesses the most numbered guests correctly wins. If the guests wearing numbers can keep a secret then this could be a very interesting and fun game.
Another game to play could be run like a pageant where the host selects a certain number of costumed guests to participate in a best costume contest, a most ingenious costume contest, and the most original costume ideas. All the other guests will get votes and the winners in each category will get a prize. You may want to avoid a worst costume contest as that may only encourage horrible costumes and could offend someone if they worked hard on a costume and it gets voted worst of the evening. Stick to games that promote positive costumes and that will make sure that the evening remains a hit and that these games will add a little more fun to the evening.
It is always fun to pick one of the more popular people in the group and help them dress in a costume that is so elaborate and ingenious that no one can identify who the person is. If you choose a couple then dress them both that way and have them wander the ball acting as if they know no one at the party. It causes an air of anticipation throughout the night as everyone tries to figure out who the mystery guests are. It adds even more to the evening when it is later revealed that the mystery couple is a couple that nearly everyone knows and the costumes were so effective that their identities could not be discovered. Games like this add a lot to the success of your next masquerade ball and can make your ball the talk of the town for a long time to come.