Ninja : "What strange abilities does this one have ?"

cowboy : "That gun remind me of someone"

wizard : "A human with magic ?"

robot : "what would the royal scientist think of you ?"

Royalty : "Why not settle this over a nice cup of tea ?"

GildedGuy : "Surely you're someone's knight in shining armor"

circus : "i never asked for a jester ?..."

Saitama : "what kind of motive is a 'hero for fun' ?"

farmer : "farming is quite peaceful, isn't it ?"

bonehead : "i yearn to have a smile like yours, comedian"

chainsaw : "the heart of a devil. betrayal does that."

nomad : "subatomic control is quite the horrifying spell."

noble : "what makes one truly noble is sacrifice."

opportunist : "now you're a soul i won't regret reaping."

luchador : "¡Ven entonces! Haz tu mejor esfuer"

salesman : "i don't need more vanity, thanks you."

diavolo : "i don't need your identity to finish you."

deceiver : "something's suspicious..."

Lumberjack : "don't get rid about what's the most beautiful about the surface."

pancake lady : "why do peoples challenge me with everything but a weapon ?"

bladedancer : "let us test your talent."

sata : "fire is my domain, not yours, deity."

Sister : "these nights have been so dark lately."

sponge : "192.112.89.113."

Senator : "why don't you back your logic with a source ?"

failedwizard : "It's clear what sets you appart from other wizards."

vixen : "a pyrokinetic monster ?... nothing new."

seelkadoom : "you have a need for speed, don't you ?"

neonwhite : "nimble on your feets, aren't you ?"

exiled : "a king needn't exile a lost soul."

Lunatic : "You're the one the flower warned me about."

Psycho : "whats with humans and blood stained knives ?"

fairytales: "if only happy endings were always guaranteed"

I'll stop for now since it take so long.

This one is very impactfull and is THE royalty easteregg

When standing still, you will naturally interact with the character named 'Air', in this interaction you will do your idle animation while being perfectly still and wasting your turns!

Revenant : "How easy it is to be misguided."

Wrath: You look human, but I can tell you're far from it.

Fallen: What is an angel without wings?

Boomeranger: What is it with children and toys?. (actual ingame typo)

Machine: Machine, turn back now.

Kirby: You look harmless, but I know what you've done.

Axl Low: Your weapon of choice is difficult to counter.

Yoyo: Children fight with toys all the time, it seems.

Netizen: Now now, no need to use brute force.

Phobophobia: I wonder what someone like yourself fears.

Mr. Pix: What's the limit to your flexibility?

Wynne: Our soul collection differs greatly.

Omen: This is a bad omen, isn't it?

Archer: Don't even try to provoke me.

Springtrap: It's upsetting you've killed more children than me...

Cryomancer: Impossible, the Glacialys has found another host?

Delinquent: Is that a toy?

Bouncer: A bodyguard? I wonder who you're guarding.

Steel: ...was that plane empty?

KungFuMan: Your fighting style reminds me of one brave child.

Slimpurt: A slime? Aren't you the weakest enemy?

Squirrel: Aren't you one of those traitors from the east?

Goat: Do you... Happen to be related to me?

Susanoo: Fusing won't give you the upper hand.

Captain Falcon: Let's see if your bounty hunter memory holds up...

ShadowRose: I wonder if my son likes roses, too.

Gallade: Using monsters to your benefit, I see that as slavery.

Grappler: A robot took your job.

Bedman: And what is YOUR task?

Fixer: They say it takes a god to break the barrier.

Staff: Is fried snow still in stock?

Bog: Impulsiveness brought my downfall. It will be yours too. (note: impulsivity is a more impactful word, subjectively; I suggest that)

Vagrant?: That's a cheap trick.

Elder: Its [sic] sad to watch humans age.

Umbra: It's raining somewhere else.

Sura: Incoherent fool.

Thaiger: Your fists will still burn in flames.

Brawler:Your eagerness reminds me of someone.

BigSword: Intimidating... but not invincible.

Oxob: You must miss being able to feel your hands.

Papaphobia: Ah, a man of belief. Reassuring, truly.

Shenn Nobi: Overconfidence will be your downfall.

Juri: I appreciate the effort.

Shin Goren: I sense something violently burning within you...

Orchi: It's hard to take you seriously.

Android: And what were you designed for, exactly?

LOV: We're both looking for what makes us human.

Bandana Dee: You shouldn't stand before me.

Insect: I never liked insects.

Kikogiri: Let's see how far martial arts will take you.

Crossbones: I'm not one with puns -- wait nevermind, I confused you with someone else.

Executioner: It is not yet my time to die.

SpaceJester: Mustn't make a fool of the audience.

Star (currently TestChar until fixed):

Deserter: I wish I had as much peace as you, soldier.

Tohno Shiki: Great, another knife.

Alfa: Experience changes a person, doesn't it?

Machina: So... you're that android I keep hearing about.

Akali: Your speed wont [sic] do wonders.

Moonwalker: You dance like the robot on MTT-TV.

Engineer: You're not the only bright mind, you know.

Pixie: You small creature, you make me pity you.

Medusa: I shan't be cast under your horrible spell.

ArcusGladius: All this effort... just to be overshadowed.

Orchid: Orchid trees are pretty, don't you agree?

Slamovich, Alvien, Nahobino, and YUPIA: It was nice to meet you... (generic)

possibly more to come!

Looking in the code:

Jinsoku: "I wouldn't envy having magic."

Judge: "Let the judge be judged."

Z Fighter: "But can I beat you, though?"

Librarian: "How much knowledge do you seek?"

Colossus: "Size won't matter here."

Shinji: "What is lost cannot be found through a wish."

Jun: "Kung Fu was meant to protect."

Hacker: "You know what happens to cheaters."

The Knight: "A discarded vessel, born into nothing."

Director: "Your deadline is coming, soon."

Prizefighter: "Singleminded. Just like the other fist fighters."

Toji: "An ex-curse user like yourself must be familiar with this situation."

Dave: "Its hard to take you seriously, anymore."

Vagabond: "You're not the first I've seen wandering."

Geometry: "You're pointless." (19 buried, none found.)

Lobo: "Death comes for us all."

Nhazul: "Hold pride in your Zetabrand clan while it lasts."

Vamp & Ire: "I reckon you don't want to see the sun as much as I do."

Ookami: "Immortal life breaches you away from sympathy..."

Niko: "I'm sorry for this, little one."

Roscoe: "Alright Gunslinger, give me your best shot."

M-O-M: "It doesn't matter what you create, nothing forgives ruin."

Seraph: "Holy flames hurt the wicked, not the innocent."

Boris: "Sorry for getting in your way."

Abel: "Do you truly believe yourself as a diety?"

Letter B: "Im out of ideas for dialogue, no one will see this anyway." (this was seen)

There is so many interactions.

Miko: I haven't seen a fox monster in a while.

Niflheim: Do you see yourself as human or monster?

Torment: No Battalion would forgive my regiment.

Skyhunter: No! I refuse to be hunted again!

Chai: When will you learn? The more you take the less you have.

Lucario: Channel your Aura. You'll need it.

Scythe: You started something greater than you think|

Executioner: It is not my time to die.

Boss: how many clones does it take to defeat a king?

Recordfuture: What happens in life isn't destined.

Yeah, 350+ of them

sukuna: the king of curses against the king of the mountain

Zero: that sword reminds me of someone.

Ronin: "How I miss being able to see the sun."

spot - "you dont belong here do you?"
Archer - "Don't even try to provoke me"
Denji - "The heart of a devil. Betrayal does that."
Sky Hunter - "No! I refuse to be hunted again!"
Lien - "Your attempt to be flashy failed miserably"
Kirin - "Put down your scythe, you're no reaper"
Sephiroth/fallen - "What is an angel without wings?"

just some that me and my friend found

Neco Arc - "You brought this onto yourself"

Here are some I've found

Pootis Engage Heavy: I don't stand a chance, Do I?.

John Yomi: Children and their "memes"... So confusing.

British Police: Humans and their false sense of justice...

Senator: Why don't you back your logic with a source?

Psycho: Whats with Humans and bloodstained knives?

Soldier: You see honor and pride within death and sacrifice.

Characters that don't have a special intro: It was nice to meet you...

I like the Scythe interaction because iirc it was the first modded character.

Scythe was not the first modded character, BUT the creator was the person that first taught me how to mod for Yomi. I paid respects in this way.