When the Cheers gang is talking about getting revenge on Gary, from Gary's Old Towne Tavern, Frasier is in his every day clothes.
The next scene, Fraiser, Lilith & Frederick are dressed up in their Halloween costumes when they come to Cheers to trick or treat and find out what prank Sam & Carla pulled on Gary.
The following scene shows the Cheers gang at Gary's to see the prank and Fraiser is back in his regular clothes again.