Character mistake: Despite being a Greek mythology buff Maxie Zeus says "Vulcan" when he meant "Hephaestus" the Greek god of fire and the forge when he first spoke with Batman.
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)
Character mistake: When Batman looks up at the computer the data of the burglaries, he says they happened "this week", but the dates are June 28, July 3, and July 13. On the screen there's also a typo; "Buaglary." (00:05:00)
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.
I've Got Batman in My Basement - S1-E20
Character mistake: One of the books Sherman is getting his detective stuff from is called "Crime and It's Causes." It must not be a very good book. (00:11:15)
Character mistake: Poison Ivy tells her beloved plant "I won't clip off any more of your beautiful petals." She clips off the whole flower, not really "petals." (00:14:35)
Character mistake: The French spoken by the waiter of the cafe is phony in a pretty atrocious way for a supposed high class restaurant. Can't even pronounce "monsieur" right, it's merely a tacked-on accent. (00:04:10)
Character mistake: Batman's computer warns him about the "air born gas emanating from river front district." It's airborne, and riverfront. (00:07:10)
Character mistake: When Batman uses his magic computer to analyze Langstrom/Man-Bat, lots of lovely gibberish appears on screen, with some notable typos such as "Bat membaaanes", "Sedum Chloride D", "Mammac higi Index Gat harmal nomeaace at padiotion." Your guess is as good as mine for the last one. (00:21:10)
Be A Clown - S1-E11
Character mistake: The magician's name on the poster is "Proscuitto", which is a wrong spelling for Prosciutto (ham). The misspelling is inconsistent throughout the episode; it is wrong the first time Joker shows the poster, then it's fixed at the fun fair and on tv. The font used is also different.
Character mistake: The news program Stromwell is watching at the beginning of the episode displays a picture of Commissioner Gordon with the caption "Comisioner." (00:02:00)
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.