Mark Hamill has stated he used this movie to delve in and get a good handle on the range of Joker laughs he could make. They're all terrifying, particularly the epic last one he lets out as Gotham's "World of the Future" explodes and goes up in flames.
The grinning corpse of the murdered Sal Valestra, as shown on the image on the right. Coupled with the Joker's demented rant at the Phantasm over a video camera, just before he detonates a huge cache of explosives in the room:
Joker: Looks like there's a new face in Gotham and soon his name will be all over town... to say nothing of his legs, and feet, and spleen, and head!
And then there's what happens when Sal makes the mistake of grabbing the Joker and threatening him; Joker's mask of mirth melts into a twisted inhuman fury◊, and the background is replaced by a solid blood red. You know from that moment that Valestra's already dead.
Immediately after, Joker plays it off like it was a joke but the way he says, "That's what I like to see... a nice big smile", you know something bad is about to happen. Sure enough, the next time you see Sal is the page image above, when the Phantasm stumbles across his remains.
It should also be noted that Sal was once a former boss of pre-transformation Joker. The fact that Sal is so visibly afraid to be in Joker's presence speaks volumes of the latter's menace. Heck, the guy actually cringes in fear after Joker's outburst, as though afraid that the clown was going to kill him then and there. Valestra also doesn't even try to call him by whatever alias he went by back then. To Sal, he's purely The Joker.
The arrival of the Joker in Arthur Reeves' office. Silhouetted in the doorway and illuminated by lightning with his trademark grin looking terrifying.
The Joker infecting Arthur Reeves with his trademark toxin.
Joker: Makes you want to laugh, doesn't it, Arty?
He immediately goes to the hospital and receives an anti-toxin but Batman appears to interrogate him which causes the laughing fits to flare up. The way he laughs through his explanation of his ties to Valestra and the implications thereof is unsettling.
Doctor: Councilman, please, you've got to control yourself! Reeves:I'm trying, for God's sake!
It's especially disturbing because he starts laughing when he feels anxious or scared, implying an increased heart rate or stress makes the toxin act faster. Joker Venom literally feeds on your fear.
And when the Joker does the deed, we should mention the cinematography. The Joker laughs demonically and maniacally while giving off a Nightmare Face, as shown here. He cackles evilly while having a soul-piercing look in his eye, and the lighting. Oh, God, the lighting. Then we see him pin Arthur to the table, and we see a close-up of his mouth as he continues to laugh.
Similarly, after the Phantasm causes Chuckie Sol to wreck his car in what we're later told is a fatal crash, the vehicle's horn is blaring. We don't see what's causing it, but the most likely culprit is Sol's dead body.
The Phantasm's theme manages to make both of these scenes straight out of horror movies, given that the Phantasm acts supernatural, especially when she goes out of the way to toy and mock the two mob bosses before killing them.
Batman’s stand-off with the cops nearly leaves him not just caught but almost killed. It’s only thanks to pure willpower, luck, and Andrea that Batman’s career didn’t end right there.
They don't show what Joker did to Andrea's father, but judging by her scream, it's pretty nasty. Having Joker just calmly walk outside and serenely eat an apple from the grocery bag Andrea dropped doesn't help.
There is something deeply unnerving about the way that Joker keeps making sexual jeers toward Andrea, calling her 'toots,' 'sweetheart,' and even refers to her as 'the babe' to Arthur Reeves. As pre-transformation Joker, he also gives her a really creepy stare and growls at her in a sexually agressive way when she visits her father.
Probably what makes it creepiest of all is how Joker still treats Andrea after he reveals herself to be the Phantasm. While you'd never expect Joker to show empathy, the man did kill her father and knew that he was the main motivation for all of the gangster murders. Yet he still sexually jeers at her and does not for one moment show any semblance of regret for having murdered Carl.
The novelization goes into more graphic details of the wounds Bruce suffers, at one point describing the entire back of his head as bleeding. When grappling with Batman during the climactic fight, the Joker "digs his fingers deep into his opponent's wounded shoulder." Ouch.
Not only is the movie's version of the Joker more terrifying than in the regular animated series, but so is its depiction of the normal 'plainclothes' gangsters.
Valestra: Either I'll have that money by tomorrow, or I'll have your heart in my hand.
The Wham Shot of Batman doodling a grin over a random mob thug in red pencil and realizing that he's the Joker, punctuated by the Joker laughing maniacally during the scene transition.
Valestra may have been a horrible person, but it’s still unsettling to see just how much he physically declined between the flashback and present-day scenes. Most of the other characters don’t visibly age much during this time frame (except perhaps Alfred).
◊, and the background is replaced by a solid blood red. You know from that moment that Valestra's already dead.
