Bottle Episode: It's just Mulder and Scully in a car, in a Haunted House, and in Mulder's apartment. And there are only two other characters beside them.
Christmas Episode: It's Christmas and Mulder and Scully spend the magical night together, chasing apparitions who make themselves known every Christmas. Cute. But Scully is somewhat uncomfortable as she is supposed to be visiting her family early in the morning.
Dresses the Same: Played with. Mulder and Scully discover two decomposed corpses under the floor and they have the same clothes as the agents. They are of course supposed to represent them.
Scully: Mulder, she's wearing my outfit.
Mulder: How embarrassing!
Scully: Yeah, well, you know what? He's wearing yours.
Haunted House: The ghost live in one. Some of the tricks are really good. The lights switch on and off, the old clock chime, the furniture is appropriately covered with dust, brick walls keep appearing in places where doors are supposed to be; there are missing stairs and ladders in the big library room, corpses under the floor, mind-screwing multiplied rooms, Christmas music keeps playing... Really quite good.
New Year's Resolution: Scully has a good one. It's something like not to follow Mulder on his crazy quests all the time.
The ghosts Maurice and Lyda died via Suicide Pact and are together in the afterlife.
The ghosts tries to get Mulder and Scully re-enact their deaths. They invoke the illusion of the bodies lying together with corpses that remind Mulder and Scully under the floorboards.
It is implied that the ghosts drove other couples to suicide. They were people who lived in their Haunted House.
Nearly played straight with Mulder and Scully who appear to have shot each other so that they need not to face their lonely lives. However, they recognize that it is a trick and they flee from the house.