How do I express sarcasm in non-dialogue text when writing a fiction novel?

Spencer sighed, the sound coming from the air itself. “It’s not really tea, of course. It’s the tangible representation, within this space, of a spell. Specifically, a spell that will allow you to communicate with Serene from wherever you are, among other things.”

“The Eye.”

“In that case, lemme have it.”

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A moment later, the barrage ended. The dome, now considerably smaller than it had been, faded from view. That sense of presence returned to the statue. “I’m terribly sorry.” Spencer’s voice sounded thinner, somehow, weaker in May’s ears. “This situation is an intolerable nuisance. May, I wonder if we might impose on you to help save Serene’s life and ensure the future of the Guild? I wish I could say you’ll be fine, but I’m afraid the odds are rather good that you’ll die.”

“Fine.” May rose from the small table. “The hard way it is.”

“Ah, forgive me once again. May, I would consider it a personal favour if you might consider doing a small task for me.” Spencer’s voice carried a note of supercilious sarcasm. “You might not die.”

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I’m…hmm. I’ve seen this question float through my feed a couple of times now, and I’m still not quite sure I understand what you’re asking.

“Think of something. Make it good, or all is lost.”

May jumped. “Don’t sneak up on a girl like that! You almost scared me out of my skin.”

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“What other things?”

In our upcoming novel London Under Veil, Eunice and I have a character who’s quite sarcastic:

“You see?” Spencer’s voice came. “My logic is beyond reproach. Iris is too important to the future of the Guild to risk. Dia and Janet likewise. The other students lack May’s outside perspective, so they are less likely to succeed. May is the right choice: expendable, but still just capable enough to make victory possible.”

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“I cannot see the future.” A hint of impatience coloured Spencer’s voice. “At the moment, I think the task at hand is rather more pressing than the past.”

May stared down at her mug, half-expecting to see some strange brew of raw magical essence. Ordinary tea filled an ordinary china cup. She took a deep breath, then swallowed the liquid. Nothing in particular happened. “Thank you,” Spencer said. “Now, off you go.”

“But I can,” May said. “You helped me out when I was in a bind, and you didn’t even know me. Besides, Spencer’s right.”

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“Your objection is noted,” Spencer said. “If we may move on to the important bit of this conversation, I would be appreciative if you might make your way over to the Eye and see if you might sabotage or otherwise distract our opponents long enough for Serene to shake off this bothersome spell that’s trying to eat its way into her mind. I would do it myself, but as you can see, I’m a bit busy maintaining this place and limiting the Adversary’s access, though I will confess to some consternation at the effectiveness with which they’ve made their way in. It must be convenient to have access to a source of energy more powerful than anything ever recorded in the history of magic. Crude, our opponents, but highly effective. Anything can be weaponized if you put enough force behind it.”

the use of remarks that clearly mean the opposite of what they say, made in order to hurt someone's feelings or to criticize something in a humorous way

Serene raised her hand. “I don’t think this is a good—”

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“May,” Serene said, “I can’t—”

“The Adversary has placed sentries of a sort,” Spencer’s voice announced, “which I expect will grow more numerous as you get closer.”

“Ordinarily I would say yes, but as the Adversary continues to gain ground in this space, I find myself increasingly constrained. I fear you will need to make your own way.”

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“I am, as I believe we have established already, a cat.”

Serene’s face hardened. “I see. In any event, as long as he remains connected to it, I cannot escape. You need to break his connection.”

“Advanced what?” She picked up speed, finding as she raced along the sidewalk that her legs didn’t tire, her lungs didn’t burn. “Is that a thing?”

Hello, I have a question about astral projection. I started to get interested in this a little while after my mum passed in april. I thought I may be able to see her and speak with her if I managed to achieve astral projection. Since this interest, every time i sleep on my back I go into sleep paralysis. However, I cant progress into astral projection because it is very scary for me as I feel like I'm suffocating when this happens. I panic and force myself to wake up. This only ever happened about once a year before this. It sometimes lasts a long time. This has happened about 3 times per week since my mum died, as mentioned on a previous post. I no longer try to go into it anymore(due to the suffocating feeling), but it still happens. I read that sleep paralysis is the pathway to astral projection. Why has this started to happen so frequently since simply taking an interest in it? Is this connected to the afterlife? I am concerned about it as I now cannot seem to stop this happening. Could it be my mum trying to communicate? Im asking due to more knowledge around this in this group.

Sarcasm is, almost by definition, dialogue. In fact, Merriam-Webster defines it as:

“You could at least try to sugar-coat it a bit,” May grumbled.

“Right. The Eye. Why can’t you just teleport me there?”

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“I’m a cat.”

“So hey, about that.” May followed the street along the bank of the river. Strange blurred figures walked along the sidewalk with her, looming threateningly over her, dim and amorphous save for their hands and legs. She shivered as she made her way around them. In the street, suggestions of cars screamed by, much too fast, as vague and indistinct as the walking figures except for the noise and stench they left in their wake. “That night you followed me home from the club…”

“So sorry to disturb you,” Spencer said. “I thought you’d want to be informed of potential threats ahead. If I’ve misjudged, please don’t hesitate to let me know.”

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“Oh, I get it! You’re being snarky.”

So I’m not sure that you can have “sarcasm in non-dialogue text,” as sarcasm is generally defined in terms of something you say or express…or perhaps I’m just not getting what you’re trying to ask.

“Lord Dormer is personally overseeing this attack on my mind,” Serene said. “He appears to be directly coupled to the accumulator. I do not know why he is not using more of the stored power within it.”

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a sharp and often satirical or ironic utterance designed to cut or give pain.

“Okay, okay, you don’t have to rub it in.” May ran a hand through her hair. “What do I need to do?”

“What?”

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“I can answer that,” May said. “They’ve already used most of that energy for something else. We still don’t understand exactly what. A directed spell of some sort, focused through a human sacrifice.”

“Did you know they would try to grab me?”

“I hardly think this is the time for a lesson on the mathematics of planar resonance in advanced multidimensional thaumaturgy.”

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“Ah, of course. Listen, this is your space, or alternate reality, or dream, or whatever the hell it is, right? You’ve already zapped me around from place to place. Why am I hoofing it to wherever it is I’m going?”

I’m not really sure how you’d convey sarcasm without dialogue, since sarcasm is, by its nature, intrinsically wedded to dialogue. It’s a form of expression.

“I’m still not entirely clear on what you want me to do.”

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“Can’t you just, like, blink me directly to where I need to be?” May said.

“Yes?”

“How?”

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“Good luck.” Serene stood. They embraced for a moment, then the air sizzled, the diagram flared, and May found herself standing, shuddering and queasy, at the foot of the skyscraper. She set out down the street in the strange twilit gloom of Spencer’s imaginary London, toward the scribble of the Thames and the sinister whirligig of the London Eye.

“If you must know,” Spencer said in a tone that suggested she didn’t, “it will allow Serene to see through your eyes and utilise you as a conduit for her spellcasting abilities. If you please.”

“No.”

Cambridge Dictionary concurs:

“Right. Okay. Focus.” She hurried along, trotting through the London that was not London, surrounded by phantasmagorical impressions of people that flitted around her in silence. “So how does this work? Is this, like, a real-time simulation? Are those weird blurs actually people in the real London right now? If someone were walking down this street in real London, would they see people where I see those—whatever they are?”

“Good heavens.” Annoyance touched Spencer’s voice. “We can’t be expected to figure out everything! You’ll have to work that bit out. Please, drink your tea.”

“There are currently some…complications. The Adversary has created a significant intrusion into this space, territory they control. Their presence is, and I do not say this lightly, quite painful. I have done the best I can.”

“What do you need me to do?” May said.

“I didn’t realise you were so sarcastic.”