Mercer and Malloy go on an undercover mission to obtain a copy of the Krill scriptures, the Anhkana, in order to understand them better, but they discover the Krill ship they've infiltrated is on its own mission: using a weapon that will kill a hundred thousand humans on a nearby colony. And the Krill have their own children aboard the ship.
- Action Prologue: The Orville answers a Distress Call from a Union colony and ends up battling a Krill destroyer.
- A Date with Rosie Palms: Alara sneaks in a subtle reference when, after Isaac offers to "attempt sexual relations" with her, she says she's "working on myself right now".
- Always Night: The Krill homeworld has intense cloud cover which blots out nearly all sunlight, resulting in their Logical Weakness described below.
- Armor-Piercing Response:Teleya: Why did you save the children?
Mercer: They're kids, with their whole lives ahead of them. They're not my enemies.
Teleya: After what they saw you do today? They will be. They. Will. Be.
- As Long as It Sounds Foreign: Spoofed.Malloy: What do Krill names sound like?
Mercer: I don't know. I don't think anybody knows.
Malloy: Probably exotic and alien.
Mercer: Probably, yeah. Like Quarz... noth, like that kind of thing.
Malloy: Zang... tozon.
Malloy: Probably not "stein."
Mercer: No, not "stein."
Malloy: Like a Haj... valorp.
- Bittersweet Ending: Mercer not only obtained the Anhkana, but he brought along an intact Krill destroyer and prevented the massacre of a hundred thousand innocent civilians. However, despite his best efforts to protect the children, he's told by Teleya that all he did was ensure they'd grow up wanting vengeance for him killing the rest of the ship's crew. It's hard to say how right she is about that, given at least Koja is shown to be curious and inquisitive.
- Blazing Inferno Hellfire Sauce: Bortus demonstrates his ability to eat anything by casually popping an entire ball of wasabi into his mouth, much to the horror of his colleagues, with Alara remarking that she'd have been left crying and throwing up if she'd eaten just half of it.
- Boldly Coming: While speaking of Alara's latest failed relationship, LaMarr suggests she date Isaac since he's as strong as she is. Isaac gladly hops on this bandwagon, as it will help his study of other cultures. She politely declines.
- Cassandra Truth: When questioned on why he and Mercer have infiltrated the Krill ship, Gordon honestly replies that they came for the Anhkana. The captain doesn't believe him, as it's far more likely they came for the experimental neutron bomb than a mere book, regardless of its importance to the Krill.
- Children Are Innocent: Mercer's reasoning for not killing the children. Plus Koja is shown to be inquisitive and questions the logic of the Anhkana, which makes Mercer that much more reluctant to harm the kids.
- Decapitation Presentation: Zazaron shows off a human head taken during a raid on a colony, then stabs it a bunch of times as part of a cleansing ceremony.
- Dirty Business: Mercer and Malloy aren't happy when they realize they have to kill the crew of the Krill ship to prevent it from carrying out its attack.
- Doorstopper: The Anhkana is a huge tome, easily half-a-foot thick. This keeps Mercer and Gordon from easily copying it.
- Dressing as the Enemy: Mercer and Malloy use holographic disguises and a captured Krill shuttle to infiltrate one of their destroyers.
- Eureka Moment: Mercer has one, while explaining to Koja about various human races, specifically about the reason for the dark skin of Africans. He suddenly realizes that the Krill, having evolved in perpetual darkness, have no natural protection against ultraviolet.
- Evil Is Not Well-Lit: Justified. The Krill race evolved in an environment with very little sunlight, which explains why their ships are scarcely lit (especially when compared to Union ships) and is supposed to be a cause of their generic unfriendliness.
- Explosive Instrumentation: A panel explodes on the bridge during the firefight with the Krill. It's responsible for fire suppression.
- Extreme Omnivore: Bortus can eat virtually anything, as the harsh conditions of his homeworld necessitated that their people be able to derive sustenance from whatever they could find. He chows down on a cactus, a napkin, and a glass to demonstrate. This may also explain why they only need to urinate once per year—their bodies produce very little waste, since they're able to process so much more than ours.
- Failsafe Failure: A panel catches fire and Mercer orders it put out. When he asks why the fire suppression system didn't kick in, Alara explains that said panel was responsible for that system.
- Frictionless Reentry: Averted. Mercer has Malloy skim the atmosphere to create a smokescreen from the reentry friction, blinding the Krill long enough so he can drop their entire complement of torpedoes onto them without them trying to dodge.
- Indy Ploy: The rough plan to snatch a copy of the Anhkana consists of "Get disguised as Krill, fly around until we find a ship or something, then find a copy and try to get out." That's also the detailed plan. Everything else has to be made up as they go along.
- Just in Time: Malloy manages to shoot down the Krill neutron bomb just before it impacts the colony.
- Mood Whiplash: Turns on a dime from light-hearted adventure and comedy to dark drama and back again several times. Although all episodes of season one of this self-described Dramedy series have elements of this, "Krill" is generally cited as a notable example due to its violence and ominous ending; yet it starts with a comedic sequence in which Bortus displays his ability to eat almost anything.
- Moral Myopia: Krill society sees anyone but them as soulless beings to be treated as nothing more than obstacles. When Mercer kills the entire crew of the Krill destroyer save Teleya and the kids to defend a helpless colony, she only sees the Krill he killed and says that all the kids will see, too. Though given Koja's vast interest in Humans and even asking if they have a soul, she might not be entirely right.
- Name's the Same: The Krill god Avis shares his name with a rental car company, which Malloy mocks constantly, such as telling the children that the humans believe in a rival deity called Hertz.
- Nice Job Breaking It, Hero!: It remains to be seen how much of an effect it will have, but Ed and Gordon's mission is this when it comes down to it. They were to obtain a copy of the Anhkana to understand the Krill and try to reach peace. In the process, they infiltrated and killed an entire ship's worth of Krill, except for children who may take it as a lesson on why humans can't be trusted. They did obtain a copy of the Anhkana, but it now looks like theft and desecration as opposed to quietly copying it page by page without anyone the wiser. In all likelihood, this mission is more likely to cause violent reprisals from the Krill, even if the goals were technically accomplished.
- Not So Above It All: When Malloy makes Bortus eat a cactus plant, Alara chastises him for possibly hurting Bortus. When the Moclan eats the cactus with no problem, Alara immediately makes him eat a drinking glass.
- Not So Different: Grayson believes this is the case with what the Anhkana and the Bible say about ownership and superiority when she first hears about the Krill faith, saying: "And Man shall have all the animals in subjugation". This, however, is an In-Universe Critical Research Failure as the Anhkana permits the genocide of other sentient beings who aren't Krill, the Bible on the other hand makes it clear to treat animals well:"Six days you are to do your work; but on the seventh day, you are to cease from your labor, in order that your bull and your donkey may rest."Exodus 23:12
"The righteous one takes care of his domestic animals."Proverbs 12:10
- That said, warped interpretations of the Bible have been used by humans in the past to justify the kinds of actions the Krill would approve of. It's possible that Krill behavior is based on similar selective reading of the Anhkana.
- Outgrown Such Silly Superstitions: It's noted that interstellar civilizations usually become more secular as they expand outward, while the Krill have remained fiercely religious in spite of it.
- Punctuated! For! Emphasis!: Teleya's last line:Teleya: After what they saw you do today? They will be. They. Will. Be.
- The Reveal:
- The Krill in the pilot episode hadn't worn helmets out of purely military necessity, they'd done so as protection from sunlight.
- We finally get to see what is presumably a Union heavy cruiser (the ship that docks with the Orville after the battle).
- Right for the Wrong Reasons: The Krill captain assumes Gordon and Mercer are on the ship to sabotage the neutron bomb. He's right in the sense that they are planning to do that, but it's not their reason for coming in the first place and it's just happenstance that they picked that particular vessel to infiltrate.
- Scary Amoral Religion: The Krill religion states that non-Krill have no souls and are therefore inferior; at best, they're tools to serve Krill interests, at worst, they're impediments to Krill ambitions that can be removed.
- Scary Dogmatic Aliens: The Krill are the fundamentalist type, attacking humans because their religion says they're justified in doing so.
- As the planned destruction of the colony approaches, it turns into a reconstruction of scenes before the destruction of Alderaan in Star Wars.
- During prayer on-board on the Krill vessel, instead of saying "Temeen Emideen," Gordon says "Katniss Everdeen."
- It's said that the Krill have clung to their religion even after developing spacefaring technology, and that if the Union were to attack them, they would see it as a holy quest. This seems like a pretty clear nod to The Covenantn in Halo.
- As Ed and Gordon are cruising through Krill space searching for a ship, they're listening to CCR's "Midnight Special"—like the driver and his passenger in the opening scene of Twilight Zone: The Movie.
- A Simple Plan: Mercer and Gordon have a simple mission: dress up as Krill, infiltrate a Krill ship, copy their scriptures. It escalates to stopping a weapon of mass destruction and hijacking the entire ship.
- Token Heroic Orc: Koja is incredibly interested in humans and even asks if they have a soul, when the Anhkana specifically states that anything that's not a Krill doesn't.
- Vampire Hunter: Invoked by an excited Gordon upon deciding that the Krill are basically "space vampires".
- Weakened by the Light: The Krill evolved on a world with virtually no sunlight, so intense ultraviolet light is lethal to them. Mercer and Gordon exploit this by rigging the internal lighting to release an ultraviolet burst, cooking nearly all the Krill onboard in seconds.
- The Worf Barrage: In true Star Trek fashion, the Orville fires all energy weapons at the Krill ship with the Worf Expy reporting "No damage." This is totally justified, however, since the Orville is a mid-size cruiser (roughly equivalent to one of the smaller "science vessels" in Trek) while the Krill ship is a full-size combat starship.
- Wouldn't Hurt a Child: Mercer calls off the plan to trip the neutron bomb inside the Krill ship when he realizes they have children aboard. As seen above, however, it may bite him in the ass later.