Best Boss Ever: Say what you will about the ridiculousness of the plot, but the final battle with Dr. Andonuts is the best part of the hack. Not only is it memorable for "Megalovania", but after beating the Id, the boss starts fighting back. He has five health bars, each with its own weakness, starting with Status Effects, then two forms for regular elements, a form where you have to reflect his ultimate attack, before finally an all-out battle with neither side holding back.
Big-Lipped Alligator Moment: At the end of the game, a ghost breaks into Varik's house just to fart on his face for no reason. Lampshaded by Varik laughing at it immediately afterwards.
The repurposed Onett map has nothing except depressing but weak enemies that drop great healing items. The boss, on the other hand…
From a story standpoint, the MagicantHub Level mid-way through the game repeatedly serves as this. The NPCs have more light hearted and funny dialogue, outside of a few disturbing remarks from select NPCs, and the appearance of the place is a lot more upbeat to look at compared to everything you tend to go through elsewhere.
Base-Breaking Character: Dr. Andonuts. Good sweet God, Dr. Andonuts! There are those who like how the game tries to explore his mind in a world where he thinks he killed the chosen four, others just view this hack's characterization as a massive insult to his character, with his wildly Out of Character acts easily flying past Canon Defilement for some, to the point he might as well have been a completely new character altogether.
The fact that the normally Useless Useful Spells are actually useful in this game. People like the fact that it averts that standard RPG cliché, while others, who feel it working on bosses is good design, feel like it was a terrible decision to make it to where they're flat out required to beat some normal enemies, since it makes the battles feel needlessly tedious and drag on for far longer than needed, especially when the game starts getting spam happy with these kinds of enemies.
Really, opinions on the entire hack over the years has slowly slid into two groups: people who think it's an interesting, darker take on the original source material, and those who see the entire thing as one giant mess of Canon Defilement-filled Narm.
If you attempt to enter the sewer as soon as you start the game, expect to die. A lot.
Similarly, if you attempt to traverse the demonic version of Winters as soon as you get there without abusing the nearby tent to heal and grind, expect to die. A lot.
Fandom Rivalry: Shares one with the Hallow's End hack. Many people who prefer Hallow's End often cite it as "the Halloween ROM Hack done right", with humor and themes often more fitting of the original EarthBound compared to The Halloween Hack, of which people often compare to a bad fanfic pile of Narm, in addition to being far more balanced gameplay-wise by comparison. Meanwhile, those who prefer The Halloween Hack often like how it tries to have darker themes than the original EarthBound, and point out how the endgame of Hallow's Endalso devolves into bad fanfic territory as well, in addition to the difficulty reaching batshit levels. Really, there are many things people prefer when comparing the two games, and that isn't even going into how The Halloween Hack treats Dr. Andonuts…
The game is sometimes known as "Push the B-Button, Stupid!" because doing so at a certain point is required to get the good ending.
Fans refer to the version of Megalovania used for the hack's Final Boss as "Dr. Andonuts's Rage". While the nickname predates Undertale, it's still popularly used to differentiate the Halloween Hack and Undertale versions of the song.
When you first encounter the Anxiety Attack enemies, they're Demonic Spiders because of their ability to spam statuses that block magic/PSI and cause characters to freeze, in addition to the fact that Varik is likely the party member you have at that point. As you progress through the game and get more party members, they become much easier to deal with. While from a technical standpoint it's because you're slowly leveling up and having more party members to fight with, it also makes sense from a meta standpoint because when you have an anxiety attack in real life, it's much easier to deal with when you have friends around you to help you calm down.
In plenty of walkthroughs, when Varik fights NO, NO and NO, he guns for the chest first, despite the supposed weakness being the crotch. And it has the same effect as gunning for the crotch. If you think about it, though, gunning for the chest makes more sense than gunning for the crotch: since Varik fights NO, NO and NO alone note actually, they're the last enemy Varik faces alone, since Paula joins the party afterwards and she stays in it all the way until you defeat Dr. Andonuts, his possible weapons at that point are either a worn dagger or a rapier, both of which are knives, and it's implied that the NOs are a Hive Mind (they have the same name despite looking different), then this strategy (gunning for the chest) sums up to Varik stabbing NO in the heart, which shuts down all other body parts due to death.
One of Dr. Andonuts' Attacks is to jed you all in the crotch enormously hard. This attack can harm Paula. Not only it's Truth in Television, as a Groin Attack harms girls just as much, if not more, than it harms boys, but in Paula's case, it really harms her more than the others, since she has the lowest Defense and Vitality (and, by extension, HP).
Harsher in Hindsight: The Remnants, who are essentiallly zombie Starmen, are shown to be melting. Undertale's Amalgamates are reanimated fusions of dead monsters that melted together.
It Was His Sled: Absolutely no one tries to hide the hack's true nature anymore. Other twists of the hack, especially anything to do with the Final Boss, are also well-known.
Informed Wrongness: Both the narrative and Dr. Andonuts himself call Varik out for trying to kill him, but Andonuts' army of monsters was massacring people and the game gives no alternative way of stopping it other than killing him.
Just Here for Godzilla: A good portion of newer players came to the hack just to hear the original version of "Megalovania".
The Dearkhart battle is supposed to be depressing because it's the Anthropomorphic Personification of Dr. Andonuts' worries that his son, Jeff, despises him. However, the impact and melancholic nature it's supposed to have is rather negated for a lot of people due to its battle musicbeingutterly freaking awesome!
The name of the final boss's ultimate attack, PSI Bitchkill Ω. Even though it will wipe out your party if you don't know how to tell it's coming and to properly counter it, it still ends up sounding ridiculous to some because of the Obligatory Swearing. Doesn't help that it usually comes in the same battle as the above drunken sailor storm.
The "NO! NO! NO!" enemies. Even though it's possibly a bit disturbing even if you're attracted to guys, it becomes a bit hilarious once you realize it can be easily defeated by kicking it in the crotch.
Never Live It Down: Dr. Andonuts is generally remembered, if not for "Megalovania", then for his constant swears. The truth is that he only swears four times during the final battle: once during his breakdown (the only one where he swears non-stop), once at the beginning of his Ice phase ("fags! you're all fags!"), through the name of his ultimate attack (PSI Bitchkill Ω), and one last time during his death (you'll get the...sh...i...). He's not nearly as bad as he's made out to be by most, yet for the reasons listed under Narm, it's pretty hard to think of anything else.
Nightmare Fuel: Remember how we said that in EarthBound, the final boss, Giygas, was the background for his battle? He returns in Dr. Andonuts' battle as the background. Fitting, as said Final Boss was encountered in the exact same machine that Giygas was stored in.
Self-Imposed Challenge: The Phaze Destrortur is ridiculously easy, but you can add a bit of challenge to it by trying to defeat it with all three party members alive. The previous two bosses can also be beaten using the non-cheap methods with high enough levels and a bit of luck.
Signature Scene: The final battle with Dr. Andonuts. Once he Turns Red for the last time and Megalovania kicks in, you hit the most famous part of the game.
That One Attack: PSI Bitchkill Ω, which can kill your entire party in one hit. Thankfully, it can be reflected.
That One Level: Twoson sewers. Even if you have the foresight to grind beforehand, the enemies there are just unfair in many aspects. They like to swarm you in groups of three, which you can't even hope to out-damage at that point in the game and several of them like to spam attacks that inflict the 'numb' status that causes you to lose your turn. Even if you're over leveled for the area, the enemies there can still easily kill you by repeatedly stun-locking you to death.
being utterly freaking awesome!