Continuity mistake: Batgirl and Catwoman are depicted without pupils, but in one shot during the fight at the Stacked Deck, they briefly gain pupils when Batgirl says "I think it's closing time."
Continuity mistake: When Selina talks to Scarface in the limousine, her eyebrows change from black to blond back to black again between shots.
Continuity mistake: Batgirl's cowl, cape, gloves, and boots are black in this episode, but in Shadow of the Bat Part II and Batgirl Returns, they are now blue and remained that way onwards.
Continuity mistake: When Selina dons her Catwoman costume, she pulls on her mask which was detached from her costume like a face mask, but later on when she returns to her apartment after the museum robbery, she removes her mask which is now attached to her costume like a hood.
Continuity mistake: At the end of the episode, Selina is wearing a purple vest and grey sweater, but they change to red and purple when she is holding Isis and watching Batman, and they change back to purple and grey as she cuddles Isis.
Continuity mistake: When Catwoman first encounters Batman during the flashback, her whip is coiled around her shoulder. When the camera cuts back to Catwoman after the shot of Batman, the whip disappears altogether.
Heart of Ice - S1-E3
Continuity mistake: When Mr. Freeze is running towards the fire hydrant, it is partially covered in a layer of ice. When the shot changes, the ice has disappeared altogether. (00:18:15)
Heart of Ice - S1-E3
Continuity mistake: When Batman breaks free of his ice handcuffs, the colors on his chest emblem are inverted. (00:15:30)
Heart of Ice - S1-E3
Continuity mistake: When Mr. Freeze's henchman Johnny gets his legs frozen, an ice "bridge" connects the gap between his feet. A few shots later and the connective ice is gone, making it look like he is wearing boots made of ice. (00:05:45 - 00:07:00)
Continuity mistake: The broken window pane on the door to the District Attorney's office changes slightly from shot to shot. When first shown, the break in the glass extends all the way up to the letter "L" in the word "law." When the shot changes, the break in the glass is nowhere near the letter "L." Also, the letter "W" in the word "law" is missing entirely, even though the break in the glass suggests a portion of the letter would still be intact if the letters were painted on the glass, as is standard. (00:10:25)
Continuity mistake: When we see Two-Face in full for the first time in the previous episode, his left eyebrow is white. In this episode, his left eyebrow is black.
Continuity mistake: When Harvey Dent is scarred in the previous episode, it's only the left side of his face and neck. In this episode and all others with Two-Face, his left hand is also scarred and discolored.
Continuity mistake: The mud stain on Harvey Dent's suit disappears when he assaults the henchman that kicked the mud on him and then reappears when he is walking away from the scene. (00:04:50 - 00:05:50)
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: During the flashback, Catwoman's whip disappears and reappears on her belt in a couple of scenes.
Continuity mistake: When she was pulling Daggett up, Batgirl briefly gains pupils when she says "Catwoman, wait."
Continuity mistake: Batgirl's cape changes length throughout the episode. It goes from reaching her ankles to her hips.
Continuity mistake: Catwoman/Selina gains and loses her pupils throughout the episode.
Continuity mistake: Harley's shoes are poorly drawn when she dances in Dr. Leland's office.
Other mistake: When Catwoman scratches Batman's face in the flashback, her fingers and claws stretch comically.
Answer: Because he stole a chemical from his lab.
But Batman knew that with it, Clayface could permanently retain his shape and Clayface desperately wanted to be Matt Hagen again. In a sense, Batman stopped Clayface from becoming human.