The Joker unleashes a lethal laughing gas in Gotham City that will drive everyone who is exposed to it for long enough to insanity.
Tropes in this episode include:
- Actor Allusion: When Batman emerges onto the Joker's ship with a breathing apparatus and stares right into Joker's periscope, we hear Vader Breath.
- April Fools' Plot: The episode takes place on April Fools' Day, an early scene featuring Alfred "drawing Bruce a bath" (on a piece of paper). Bruce retaliates by the episode's end by pretending to take the priceless Ming vase Alfred broke out of his salary.
- Art Shift: The animation is noticely more rubbery and cartoony than most any other episode which actually fits as an April Fools episode with the Joker.
- Berserk Button: Joker really is outraged over the "death" of Captain Clown.
- Breaking the Fourth Wall: The Joker goes out of his way to tell the viewer as he readys to loot the financial district, When the going gets tough... the tough go shopping!!!
- Cape Snag / Giving Them the Strip: A version of Batman's detachable clasp is shown when his cape becomes trapped in the grip of a robot Joker henchman—Batman quickly detaches his cape and spends the rest of the episode capeless.
- Cut Lex Luthor a Check: Joker creates a submarine with a trash barge over it that profusely emits his laughing gas along with a fully functional killer robot... and robs one diamond truck and loots a couple stores in the financial district. Justified in that driving Gotham mad could easily be the main objective and any looting involved is just a bonus.
- Determinator: Captain Clown takes a ridiculous amount of crowbar shots to the head. Being a robot helps with that.
- Disproportionate Retribution: Inverted; after Batman destroys the Joker's pet robot, Captain Clown (which Joker considers murder, since Captain Clown was his best friend), Joker retaliates by... dumping a forklift full of smelly garbage right on top of Batman.
- Getting Crap Past the Radar: Captain Clown's Mecha-Mook status allows for him to be dispatched in a manner that'd be impossible to show with your standard flesh-and-blood henchman. It also allows Joker to avert the Never Say "Die" clause and chastise Batman for "killing" him.
- Jokers gas typically causes people to die laughing maniacally with a large grin on their corpse. This version apparently only causes permanent insanity if exposed for too long.
- Hoist Hero over Head: Captain Clown lifts Batman over its head and starts spinning him around very fast before dropping him in a trash can.
- I Know Kung-Faux: One of Joker's goons tries to intimidate Batman with quasi-martial arts posing, yelling, "Hi-ya!" Batman effortlessly puts him down in about 3 seconds.
- Large Ham: The Joker gets a few extra-hammy lines: "You KILLED Captain Clown!!!!" and "You're going to melt just like a grilled cheeeeeeeeeeeese sandwich!!!"
- Mecha-Mook: The "Captain Clown" robot piloting Joker's laughing-gas barge. Also a Giant Mook, given its strength.
- No-Sell: Captain Clown is a rather durable robot; Batman hurts his fist trying to sock it, and in a later scene, even whacking it upside the head with a crowbar barely slows it down. Eventually, he has to lure it to some heavier machinery—a trash compactor—and manages to crush it.
- Not So Stoic: Joker is dangling over the fire and pleading to be saved. Batman would never just let him fall, but he's okay with pretending to consider it and hearing him beg first.
- At the beginning of the episode, Bruce is nonplussed over Alfreds drew you a bath gag, prompting Alfred to say, Not a funny bone in that mans body. At the end of the episode, he suggests garnishing Alfreds pay for a couple of years to pay for the vase he broke while affected by the gas only to note hes just trolling Alfred.
- Priceless Ming Vase: Alfred, under the influence of the laughing gas, smashes a Ming, and is even prepared to accept being docked pay from Bruce Wayne as punishment.Bruce: Don't worry about it. I'll just take it out of your salary for the next couple of years.
Alfred: [Oh, Crap! face; then, resigned] Yes, sir.
Bruce: Alfred... April Fools.
- Punch! Punch! Punch! Uh Oh...: When Batman realizes that Captain Clown is really a robot.
- Robotic Reveal: If the constant whirring every time he moved didnt give it away, Batman eventually destroys Captain Clowns Mask to reveal a robot underneath.
- Save the Villain: Lampshaded when the Joker is hanging over a pit of molten metal.Joker: Batman! You wouldn't let me fry, would you?Batman: (considers it)Joker: BATMAN! (Batman pulls him up)
- Shout-Out: After dumping Batman underwater, Joker turns to Captain Clown and says, "Well, Captain, this could be the start of a beautiful friendship!"
- Shower Scene: After Alfred pranks Bruce by "drawing" him a bath (on paper), Bruce hops into the shower instead, then leans his bare torso back out to ask Alfred to turn on the radio.
- Soundtrack Dissonance: The episode has a rather minimalist soundtrack: a drum machine straight out of a really dark hip-hop video, with the Joker's regular theme interrupting throughout. It's actually very unsettling.