Accidental Innuendo: If you hit Ralsei's dummy too many times in the combat tutorial, he'll say that "... if you want to hit me, that's okay, too!" It's due to his Extreme Doormat personality, but given how he blushes while saying that, some players joke about him having… ulterior motives, not helped by all the intentional Ship Tease between Ralsei and Kris.
The King ups the ante from Undertale in, well, spades. He consistently messes with your dodging area in ways that would have Sans taking notes, forcing you to stay moving, and has an absolutely badass Boss Remix of the Card Castle music to go with it.
The superboss of Chapter 1, Jevil, due to being akin to the absolutely brutal exclusive bosses from the Genocide route of Undertale, along with his battle theme being considered on-par with King's theme.
The minor bosses are no slouch in the creativity department either. Susie and Lancer fight as a team, complete with a Popple and Rookie-esque duo attack, and the second fight with K. Round implements a trajectory system just so you can hurl Ralsei at it for a speedy victory.
Demonic Spiders: Bloxers hit like trucks, capable of taking down Ralsei in two hits and Kris in three, and their attacks can form hard-to-avoid patterns. The method to defeat them non-violently, while an interesting gameplay change, can take quite a while if your timing isn't good enough, and the fact that you only have two party members when they show up doesn't help. They're about the only enemies that can cause problems during Chapter 1, aside from the later bosses.
Fan Nickname: While not as common as "Delta2ne" for Chapter 2, "Delta1ne" occasionally comes up as a retronym for Chapter 1.
Fountain of Memes: The superboss of Chapter 1, Jevil, is absolutely one of these. It probably has something to do with his ridiculously catchy boss music, as well as his highly quotable dialogue and voiced sound clips.
Jevil: CHAOS! CHAOS! I CAN DO ANYTHING!
Moral Event Horizon: The King crosses the line when he initiates a Wounded Gazelle Gambit to feign defeat so Ralsei can heal him, just to get one last shot at killing the heroes.note He does threaten to throw his own son Lancer off the roof earlier, but Chapter 2 reveals this was an empty threat and he knew Lancer would be fine, but it's still seen as appalling and abusive that he would threaten his life to begin with.
Nightmare Retardant: When you first fall into the Dark World and see the silhouette of someone watching you, you just know it's going to go badly — cue the creepy chase music as the figure begins to hurl missiles at you and Susie, forcing a frantic dash for safety. The second time through? That's Lancer. You know exactly who that is and it'sLancer. It's probably the only time in the story he puts on a plausible bad guy performance.
One-Scene Wonder: The superboss of Chapter 1, Jevil, enters and exits with the sudden brevity of a matchstick, and his relevance to the overarching story is only expounded upon by Seam in an optional (and easily missable) conversation. However, he became an instant hit among fans thanks to his catchy fight music, frustrating battle, and Crazy Is Cool appeal.
When the game was only SURVEY PROGRAM.EXE and you tried to install the game, your computer may have thought you were installing a virus on your machine.
Kris' bullying at school, particularly Susie's attempted murder, can remember painful memories to some people, especially if you consider they're the only humanin a monster town and that this has uncannily palpable consequences on their daily life: their thoughts show that they seem disconnected from the rest of the world (which is a disturbingly realistic portrayal of dissociative disorders), and the scenes where they tear their SOUL out are not much different from a lonely teenager harming themselves.
Signature Scene: As the number of tropes related to him would clue you in, the superboss fight against Jevil is the most discussed scene of the chapter, due to setting up several implications about the world the characters live in and in hindsight, unique aesthetics, and beginning trends found in the future superboss fights.
That One Attack: Jevil fittingly has a large amount of troublesome attacks, but his ring, carousel, and scythe attacks stand out the most. The first one of these summons a bunch of spades and encloses them one after another in the circle, and is very hard to dodge without some luck or knowing which one to dodge first (and this is his second attack, by the way). The second of these takes up a lot of the dodge window and moves up and down almost as fast as your SOUL does, not to mention its hitboxes are somewhat distorted. The last requires you to quickly move away from the center to avoid the first volley of boomeranging scythes, and they keep rotating in and out very quickly; the second time he uses it, Jevil will throw out massive straight-moving red scythes that you need to avoid alongside the rotating ones.
