Mad T Party and Freeze the Night have some similar elements, but are different. It is still a dance/music party, but there are some big differences. Mad T Party had a live band, which alternated with a DJ. Freeze the Night only has a DJ. There are dancers which come onto the main stage periodically, but they remind me more of the Hottest Deck in Town than the Mad T Party Band. There is also a much larger emphasis on Freeze the Night being family friendly and focused on families. There is less emphasis on alcoholic drinks at the booths. I saw a lot more kids on the "dance floor". They had an ice carver making ice sculptures; she comes out 4 times per night at 20 minutes after the hour (e.g., 6:20 pm, 7:20 pm, 8:20 pm, and 9:20 pm). I thought that was the best part of Freeze the Night. While Freeze the Night was fun to check out, I liked Mad T Party a lot more.
As PPs have said, Marshmallow is generally out at the start of the party. On Saturday night, they didn't uncover him until about 10 minutes after the party started, but on Thursday he was uncovered from the start of the party! I didn't see any CMs making him move while I was there, so he was just a static photo op. They did have a PP photographer in the area.