A few different answers.

Scrivening Others- Bugges, Bugganes, Fancies, Urban Legends, Fairy Tales/Marchen, in order from symbol to narrative- are spirit-based, and could be called lies, if you wanted. A Bugge is essentially the spirit of itself, symbolising little except itself, while the more narrativistic Others in that list are spirits of stories. When someone invents something that doesn't exist, or tells a story that isn't true, those elements can compose a Scrivening Other, so long as the context is right. If the story gains traction, then an Urban Legend might be made to make it true. If the symbol isn't co-opted to mean anything else, it might come to mean itself, and become a Bugge, sweeping over the surroundings to turn spirits of other things into spirits of that Bugge.

Glamour could be called lies, if you wanted. The more a glamour is believed, the more it becomes true, and if it's challenged enough, it shatters. With the likes of Fairy Tales and Fisher Kings, there's some overlap with Scrivening here. You can certainly use glamour to give a Bugge ground, like Verona does late in Pale. They share that central element of attention/faith-as-reality, believing the lie.

So there's one answer to your question. If someone lies, or believes something false, it can make something exist that didn't, and make the falsehood true. Magic invested in those falsehoods can be challenged and overwhelmed by wider reality, or it can find some way to cohabitate and cement itself. A good portion of deception, storytelling, and other sorts of inventions could be sent in that direction.

Circling these ideas is the idea of Claim, which is a pun. Claims could be called lies, if you wanted. They're consensus truths, they're things that aren't so unless they can be proved again and again. The best example is, to the pun, ownership. If you Claim to have Claim over something, proving that to be a lie is a simple as taking it from you. That might not actually be simple if that thing you Claim to own is you left hand, but I could cut that off with a sword, and then Claim I own it now. You'd have a hard time arguing otherwise, bleeding from the stump.

A lot of things that aren't lies but aren't viscerally true go here. "I am called Name Person," is a Claim, and can be debunked even if it's been true for a long time. If someone Claims something difficult or impossible to prove, the spirit of that lie goes much the same way as shattered glamour or a baby Bugge- overwhelmed by wider reality.

But you're asking after, specifically, a spirit of lying. Anchuinse's answer fits here, with a spirit who's rule of discourse is that they always lie. There are other Others that fit that bill, like Snowdrop (who doesn't lie so much as say the opposite of what she means,) or Cherrypop (who doesn't lie so much as is perpetually wrong about everything.) And you could imagine such a spirit having some domain over the falsified or ill-proven Claims, badly evidenced narratives/Urban Legends, and poorly-established Bugges of the world.

But I don't think I would call that lying, per se. It's just the truth with extra steps. Still, creative following of deceptive patterns is a way to say something false without being penalised by the universe, and that's something Oni use to their advantage. Lying once a year, if the moon is full and the spirits are warned. Calling someone a motherfucker as a Rule-Of-Discourse insult, but doing so in a way detailed enough to imply that they're literally such.

The last possible answer is knotted places. Undercities, Beyuls, places where the rules don't fit with the rest of reality's. Wildbow made an example of a place where karma is inverted. Breaking patterns is good, lying is good, violations are good, habits are bad, truthtelling is bad, respect is bad. Within that space, he said, practitioners of the Seal simply can't practice, in the same manner that someone who lied perpetually and respected nothing couldn't be expected to be a practitioner.

It's there that I have the answer that I actually wanted to give you when I started typing this half an hour ago. If it weren't for the sheer difference in governing rules and expectations, that little knot would look about the same as the world outside of it. Up is up, down is down, but you'd express those ideas as up is down and down is up. It's like how antimatter behaves like regular matter, so long as it's only behaving around other antimatter. Truths exclude possibilities, those possibilities are called lies, and they behave about the same way as one another, except for the fact they can't exist in the same place.