If it weren't for the festivities, the Doctor would've been really concerned for all the spooks running down some halls and some eerie banter between others, trying to scare each other. There were even some heavy footfalls that made him pause and wait to see if it was what he was thinking, and relieved to find out not.
He didn't have a costume himself, opting to just wear a black suit rather than his brown pinstripe one. Now was a great time to explore the prison while everyone was distracted, but he wanted to see everything first.
The Doctor made his way through the activity areas, avoiding the face painting, and looked a little around the dance floor, but chose not to participate there if he could help it.