Costumes
Costumes are the replacement for Pixel Effects and were first released during the Haunted Carnival campaign in October 2012. The only major difference between Costumes and pixel effects is the fact that Costumes don't cost Pixels and tend to last a longer length of time.
Costumes released during the Habboween 2012 campaign did cost Credits and Pumpkins, although users could gain a free "Alien Costume" by going to a Staff Owned Room called "BECOME bobba". Once a user has purchased a costume, they can choose to active it under the Clothing and Appearance section and it will last 30 days once activated.
Just like pixel effects, you cannot trade Costumes.
Costumes
Here are all the costumes that have been available so far (excluding the handful that were previously a pixel effect and simply recoloured/given animation):