Other mistake: The Scarecrow and his goons escape on an airship, which has the control bridge in the gondola under the main structure. Batman reaches the top of the airship, and so does Anthony the goon...but he does it from a trapdoor on the roof of the gondola. There's a whole structure in between he skipped. (00:15:10)
Continuity mistake: Batman knocks the tommy gun off Anthony's hand. He is looking at the weapon that lies on the blimp, and then tries to seize it again. The weapon is positioned different between the two shots. (00:15:25)
Continuity mistake: Batman got rid of the two goons through non-lethal falls, and he is about to face Scarecrow. Scarecrow has his escape planned; he has his right hand on a lever by the armrest...or in the next shot, on a lever above him. (00:18:05)
Character mistake: When Batman gets the information from the computer just in time to wrap up the episode neatly, the computer misspells the word "Professor." (00:19:40)
Other mistake: Gordon has some impressive ceiling fan in his office, since not only one of its blade supports a full-grown adult hanging by the back of the neck to it, but it even keeps working as usual during it. (00:21:30)
Continuity mistake: Scarecrow's boots start out dark red then they're light brown later in the episode.
Continuity mistake: Batman tears off the front of The Scarecrow's collar. Yet later in his hideout it's fine again.
Be A Clown - S1-E11
Continuity mistake: The Mayor is giving an inauguration speech. Look at the crowd in the long shot. It cuts closer, and you can see that the man in cowboy hat that was in the crowd moved behind the mayor on stage. A journalist in red tailleur also switches to lilac. (00:01:20)
Be A Clown - S1-E11
Continuity mistake: Summer Gleeson points the microphone at Mayor Hill while she has her left hand on a broken beam that is either absent or at different angle when they pull him out of the rubbish. (00:02:50)
Be A Clown - S1-E11
Continuity mistake: Joker splats a full cream pie on the mayor's face. When he walks away, the screen has mostly cleaned itself. (00:03:40)
Be A Clown - S1-E11
Revealing mistake: When Mayor Hamilton Hill speaks to his geriatric butler as he is tying up the birthday banner, the butler's right hand is miscolored in some frames and becomes part of the banner, same purple color. (00:03:55)
Be A Clown - S1-E11
Continuity mistake: The first time we see Jordan in his room, a huge monstrosity of a doll is propped against the door. This puppet reaches the knob of the door while in a sitting position. Then a few seconds later his dad enters the room, and the doll is at his ankles. (00:04:00)
Be A Clown - S1-E11
Continuity mistake: Jordan puts down his hat when his dad arrives. The hat is on opposite ends of the table between shots. (00:04:25)
Be A Clown - S1-E11
Revealing mistake: At the beginning of the shot with the creepy clown that sends his unicycle crashing and begins juggling, the kids in the background are frozen in place for the first frames, then start moving. (00:05:15)
Be A Clown - S1-E11
Continuity mistake: In the overhead shot of "Jekko" that pushes the cart with the cake, next to a waiter with a red towel there's a man in an orange shirt. Next shot and his shirt is blue. (00:07:55)
Be A Clown - S1-E11
Continuity mistake: When Bruce Wayne plays clumsy and fends the crowd with his large package, the same people (like the elderly woman with the big hat) move out of his way multiple times in different shots. (00:09:05)
Be A Clown - S1-E11
Continuity mistake: The VHS tape on top of the TV screen is positioned 90° differently between the opening shot and the next. (00:11:05)
Be A Clown - S1-E11
Other mistake: The cards that Jekko the Jokester throws at Batman have in one shot ("Now it's my deal") numbers that do not match at all the symbols. (00:13:40)
Be A Clown - S1-E11
Revealing mistake: When the tied up Batman is forced to emulate Houdini, he draws the air that will last him for the two minutes of his act while water already submerged his face. (00:15:15)
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.