Continuity mistake: Batgirl's boots gain and lose heels throughout the climax of the episode.
Continuity mistake: When we first meet Harley Quinn, her gloves are white before becoming their normal colors of black and red in the next shot.
Continuity mistake: Both of Harley's shoes are red as Batman holds her after rescuing her from falling.
Continuity mistake: During his introduction Scarface's scleras go from light yellow to white then back to light yellow.
Continuity mistake: When Poison Ivy is introduced in her trademark green costume, she's bare legged. Yet a few shots later, she's suddenly wearing green tights. While she's offscreen for a brief period, there's not enough time between the shots for her to have put them on.
Continuity mistake: The 10/6th on the Mad Hatter's mind control cards come and go throughout the episode. An example is when he first is shown holding them they're blank. Then when he decides to use them on his date with Alice they've suddenly got the 10/6th.
Revealing mistake: When the passengers are evacuating the sinking ship after the bomb goes off, there is a shot shown from above, of passengers running up the stairs. Many of the character designs for the passengers are repeated throughout the shot. For example, a blonde woman in a purple dress can be seen three times in the shot. (00:02:36)
Continuity mistake: Scarecrow's shoes are light brown in most of the episode. Yet once he's back in his cell they're suddenly dark grey.
Continuity mistake: When The Joker's going down the garbage chute he's riding down on his butt yet somehow he's on his stomach after a shot of Batman is shown.
Continuity mistake: Batgirl and Catwoman briefly gain pupils in one shot of them during the Stacked Deck fight, despite not having any throughout the episode. (04:00:39 - 04:41:24)
Continuity mistake: Batgirl's cape changes length throughout the episode. It goes from reaching her ankles to her hips.
Continuity mistake: The 10/6's on the Mad Hatter's mind control cards come and go throughout the episode.
Continuity mistake: By the time Batman gets to Ivy's garden, his cape and hood are blue, but turn to black a few seconds later.
Christmas With the Joker - S1-E38
Other mistake: Once Joker's back in his Arkham cell he should be wearing prison pants again like he was at the beginning of the episode. Yet he's still in his purple pants.
Continuity mistake: Bruce's robe goes from a light purple to mint blue while he's talking to Alfred at the end of the episode.
Character mistake: The Scarecrow's thugs flee as his water pump machine explodes, yet he seems to have stuck around long enough to be affected by his own toxin.
Answer: She escaped off-screen and created a copy of herself to fool everyone.