Plot: In revenge for making him late, Temple Fugit wages a terrorism campaign against Mayor Hill, and will kill Batman if Batman gets in the way.
This is one of my favorite episodes, and the reason is almost entirely the Clock King himself. He's everything a minor Batman villain should be, themed from weapon to location to McGuffin to horribly punny real name, a mental threat, capable of creating real traps and dead ends, as well as a physical threat, more than able to defend himself when Batman comes to punch him.
There are only two moments the Clock King is not ahead of Batman (when Batman uses the dueling deathtraps of a bomb and vacuum pump against each other to escape, and when Batman redirects the Clock King's cane into the gears of the clock tower). Otherwise, the Clock King completely controls this episode, from the street lights to the trains, to knowing Batman's every move and piece of equipment and being prepared for anything.
The animation for this episode is possibly the best yet. Each sequence, from the ever worsening flashback at the beginning, to the escape from the bank vault, to the train crash, is expertly done. But the final fight in the gears of the clock tower is exceptional. Totally surreal, completely illogical (really, throwing one gear out of joint causes the whole thing to crash?), but perfect for a cartoon fight and a Batman cartoon at that. It is an utterly mesmerizing episode.
My only real question is why this is not the first Riddler episode. I mean, look at the Clock King, bowler hat, sharp suit, on-theme cane/sword: he's basically a palette swapped Riddler in design anyway. He behaves in a very Riddler-esque style, leading Batman into death traps, taking control of the city's systems and using them to his advantage, basically playing a very deadly game of chess with the city's protectors. The Riddler will even be introduced in a very similar Revenge plot episode (though the Riddler will be SLIGHTLY better justified). So why use a great Riddler plot on a minor villain?
Especially since, like they had with Mr. Freeze, they were basically inventing the Clock King anyway. There is a Clock King in the comics, a Green Arrow villain who made his way onto the Adam West tv show for two episodes, but that's a completely different character, with a different punning real name (William Tockman). That character was an incompetent crook who used clock themed weapons badly. He had none of the (Riddler-esque) character ticks this Clock King exhibits, the emotionless demeanor, the machine-like command of facts and details, the absolute disdain for inefficiency and improvisation. So if they were going to create a character who acts just like the Riddler, why didn't they just use the Riddler?
This also represents the first time Batman has saved Mayor Hill directly. Yes, he saved Jordan Hill, but it's unclear if the Mayor knows Batman was there, or that his son was ever in any real danger. One wonders if his opinion of Batman has changed since the first episode, where he ordered a manhunt for Batman.
Also, like Clayface, the Clock King simply escapes at the end of the episode, leaving the plot unresolved. It's not clear why he would stop trying to kill the Mayor, or why Batman would stop looking for him. But the Clock King won't be for awhile, and Batman won't even think about him until he reappears.