"So you are the one who invited me here."
Here are all of Hassel's quotes in the Indigo Disk DLC, where he appears solely in Blueberry Academy's League Club Room as a special coach (200 Blueberry Points required!). I collected the quotes mostly from my own playthrough, as I found his quotes page on Bulbapedia a bit lacking in the DLC section at the time. (That page does have an almost complete collection of his quotes in the base SV game, so I won't list them here unless people ask me to.)
Entering the club room:
"Greetings. I am Hassel, the art teacher at Uva Academy--as well as a member of the Elite Four. It is such a pleasure to be able to meet all the fine students at Blueberry Academy."
First visit:
"Ah, young Player. So you are the one who invited me here. To think that in the brief time since I last saw you, you'd gain such an important role at this school... It-it's so surprising! And I'm so habby for you... I... I just..."
(Player: "Please don't cry"/"Uh, Mr. Hassel?")
"...I'm very close to tears, but I'll do my best to hold it in for now. I don't want to scare the other students here, after all."
Battle:
"Say, young Player, would you be willing to have a battle with me?"
("Yes") "I'm excited to learn just how strong you've become."
("No") "Ah, perhaps another time, then."
(sending out Baxcalibur) "A painting isn't finished until the final brush stroke. Let's complete our work together!"
(terastalizing) "It is time to don the crown of dragons! Let your color blot out all else!"
(using Glaive Rush) "Pardon us for backing into you! Baxcalibur, use Glaive Rush!"
(losing) "The mighty dragon has been felled!"
(after battle) "Thank you for the battle! I think someone with such skill deserves a little treasure from the dragon's hoard. I'm happy to battle you anytime, as long as you feel you have something to learn from me."
After first battle:
"When I faced you at the Pokémon League, your strength was a work in progress--you still held potential that had yet to be fully realized. But now...it has become so...so unshakable.. You'b...you'b come so far...I--I just can't... BWUUH huh huh hoi hoi!"
(You came up with the Moved to Tears emote by watching Hassel!)
"I hope you continue on your path with a sense of freedom-and of humility."
Second conversation with player:
"I can't express how pleased I am to have this opportunity to teach at another school. Although I wonder... What does this academy need of me? Am I here in my capacity as an art instructor or as a member of the Elite Four?"
("An art instructor!") "I would hope so, but the students' reaction to my last art lecture seemed... lukewarm. Perhaps it was my imagination, though."
("An Elite Four member!") "Ah, I should have known! That would explain the lukewarm reaction I got when I held an art lecture..."
"You know, I have heard that Blueberry Academy places a strong emphasis on the study and practice of Pokémon battles."
"I think that for my next lecture, I will invite Professor Gible and do something a little bit more hands-on. Thank you for your input."
Third conversation with the player / trade:
"I've been told that the students here at Blueberry Academy voluntarily take active roles in various committees--and even help run the school! I suppose it's fitting that a new school like this one would be so boldly experimental."
"I admit, though, that I personally have my doubt about saddling students with such responsibility. It seems a rather great burden to place on them when they are still so young..."
("How's that?"/"Go on...?") "Well, youth is the only period of life in which one may indulge in play without a care in the world.
"In that sense, I worry about you too, you know."
"Please do take care not to overburden yourself with expectations of others. Ah, but I do apologize... As I get older, I seem more prone to offering unsolicited advice. Now, how about we make things more cheerful--with a Pokémon trade, perhaps?"
("Yes") "Thank you kindly for humoring me. Now, I would like to offer up a fine specimen of an Arctibax."
"Hmm... It’s not wise to trade when you only have none Pokémon with you.See to it that you have at least two Pokémon in your party, and then we can trade!"
"You're willing to trade your ___ for my Arctibax, then?"
("No") "Please don’t hesitate to come speak to me again should you be in the mood for a trade."
("Yes", after trade) "___ is a fitting Pokémon indeed. I would expect no less from you."
"I will be sure to take very good care of it."
Conversations with the player:
"All the students here at Blueberry Academy are so nice. It is truly a pleasure to teach them."
"It feels like you've grown more and more each time I see you. It's enough to bring a tear to this old man's eye..."
"You know, I saw Brassie on one of those big TV screens in Levincia. Doesn't it make you happy to see a friend giving it their all?"
"The ___ you traded me is just the sweetest thing, Player. It seems happy to serve as a model for my paintings!"
"How is Arctibax doing, by the way? He loves belly rubs, so don't be afraid to give him a good scratching from time to time!"
Conversation with Drayton:
Hassel: "Why, if it isn't young Drayton! I didn't know you were a member of this club."
Drayton: "Gwuh! Mr. Hassel?!"
Hassel: "Your grandfather Drayden informed me that you were forced to repeat a year of school... Several years, in fact!"
Drayton: "Yeesh. Thanks for letting the whole world know, Grandpa..."
Drayton: "Fine, so I got held back a couple times! It is what it is, all right?"
Drayton: "Doesn't life have room for taking a stroll on the scenic path sometimes?"
Hassel: "Indeed. But studying is also an excellent way to broaden said path, is it not?"
Hassel: "I am not suggesting you should desperately try to live up to the expectations of others."
Hassel: "I simply hope that you spend your days as a student in a way that you do not regret later on."
Drayton: *sigh* "I get it, Mr. Hassel, I get it. Please just give it a rest already."
Conversation with Brassius:
Hassel: "Thank you so much for your kind participation in my class the other day!"
Brassius: "Well, it would be unimaginable to turn down a request from my dear ol' Hass."
Hassel: "You know, I imagine you would make a fine teacher in your own right, Brassie."
Brassius: "No, never... These impressionable youths would be too great a burden for me!"
Brassius: "Taking on the responsibility for such young, budding lives... It is a weight I could not bear."
Hassel: "Indeed, being a teacher means shouldering the weight of that responsibility! I admit it's not easy."
Hassel: "But that is why watching the growth of my students makes me cry tears of joy!"
Brassius: "Truly, you were born to be a teacher, my dear Hass."
Conversation with Larry:
Hassel: "Honestly, Larry! Always with the poor attitude! Is some enthusiasm too much to ask for?!"
Larry: "... ... ..."
Hassel: "Larry? Larry! Are you even listening to me?!"
Larry: "If I answer honestly, will it make you angrier?"
Hassel: "...What do you mean?"
Hassel: "Being honest is commendable! Why, it may help calm me down rather than make me angrier."
Larry: "Well, I was asleep just now, actually."
Hassel: "GRRRAAAGH!"
Conversation with Rika:
Hassel: "Whenever I'm deeply moved, I can't help myself--the tears just flow like waterfalls!"
Rika: "Aw, but that's a good thing! It means you've got a warm, caring heart... I think?"
Hassel: "Ah, but I do waste so much time crying! If it weren't for you, we'd never be able to finish any Elite Test!"
Rika: "Oh, don't worry about it! I love talking and keeping things moving and all that!"
Hassel: "Is that so? I'm a little surprised--I'd have thought such duties would be painful for you. After all, you are normally rather prone to clowning around..."
Rika: "Wait, clowning around...? I'm the only Elite Four that gets anything done!"
Conversation with Poppy:
Poppy: "Grandpa Haaasselll!"
Hassel: "Hello there, Poppy. Are you working hard as a coach?"
Poppy: "Yes, I am! I know I'm still small, but I'm doing my very, very best!"
Hassel: "Oh, I'm so proud of you, Poppy! You're but a young child, and yet... You're--*sniffle*--worgig so hard...wid all de adults... Such dedigashun... BWUUUH huh huh huh huh! HUUUUUUH huh hoi hoi hoi..."
Poppy: "Oh no! Another one of your crying fits, Grandpa Hassel?! There there, don't cry. I'll give you a hug!"
Conversation with Geeta:
Geeta: "Hassel... Is there anything troubling you regarding the day-to-day operations of the League?"
Hassel: "Anything troubling me...? Hmm, well... The bell that tells us when it's time to enter the Elite Test room has been broken for a while. It would be nice to get that fixed."
Geeta: "Ah yes... It's been several months since it broke now, hasn't it? I apologize for the inconvenience. I have already contacted the repair crew, but their schedule is unfortunately completely full..."
Hassel: "I suppose everyone is very busy nowadays. It's not a high priority, to be honest. We just shout to the next Elite Four member when it's their turn to battle. It's just that--"
Geeta: "Say no more, Hassel. The problem is Larry, correct?"
Conversation with Nemona:
Nemona: "Hey, Mr. Hassel! Did I tell you I've been training a Kommo-o?"
Hassel: "Ah, the Scaly Pokémon Kommo-o! A unique dragon indeed!"
Nemona: "Yeah! I met it in Kitakami--and it's awesome! I wanna try all kinds of strats with it!"
Hassel: "Then allow me to offer some advice!!!"
Hassel: "You must utilize its defenses and use Clangorous Soul the first chance you get!"
Hassel: "Accomplish that, and the scaly dragon will indeed become your key to victory!"
Nemona: "All right! I LOVE victory! I've been thinking a lot about what other moves to teach it! Can I run 'em by you?"
Hassel: "I would be more than happy to offer my input."
Other characters mentioning Hassel in the DLC:
Brassius: "You have had the opportunity to take Hass’s classes back in Paldea, have you not? You should be aware of how lucky you are as you make your way in life."