No one asked for this, but here's my opinions/theories on deltarune Asriel.
I think he'll be the character with the biggest difference in personality from his Undertale counterpart. Most of the characters, if they have differences, they're just different circumstances. Bratty and Catty aren't friends, for example, but they would make great friends still. But Asriel, I think, has been shown to have a different characterization, in my opinion, and it mostly amounts to one big thing.
UT!Asriel is very timid, and DR!Asriel seems much more bold. In Undertale, Asriel notably isn't making a lot of decisions for himself, and even goes along with Chara's plan even when he stops agreeing with them because he's too timid to go directly against them. He does, later, when he keeps control of the body to prevent Chara from killing humans, but he let it go for longer than he should have. In addition, as Flowey, even when he was thinking of killing people and felt no compassion for them, he was timid about it at first.
DR!Asriel, in comparison, has shown a relative boldness, even in the few stories we hear about him. He's making more decisions for himself, and even kisses someone even knowing his parents wouldn't approve. Some of that might be the age difference, since UT!Asriel was pretty young and DR!Asriel is college age, but it is still a notable difference that many of the other characters aren't affected by.
One of the interesting differences in circumstances for Asriel is his parents' divorce situation. It happens in both universes, and for (What I believe to be) very similar reasons. So in Undertale, Asriel dies before his parents separate - it's part of the situation that sparked the breakdown of their marriage. But in Deltarune, he witnessed them before, during, and after the divorce. His reaction to it is also interesting, and I suspect this might be another characterization difference. I don't know how Flowey felt about children dying, since he wasn't really around for that bit, and he just popped back up long into his parents' separation - but he didn't feel anything towards them anymore, so there was no reason for him to be bothered by it. He was completely separate from the situation (I am playing with that a little in the CoreSoulsAU). DR!Asriel was not only directly affected, but also had to watch Kris be affected by it as well. They're very close, so I think that would majorly affect his reaction to everything going down. So here's my take on the situation (up to Chapter 2):
Asgore was police chief when something happened to Dess Holiday. My read on it is that there was some ambiguity over whether or not the negative outcome of the situation was Asgore's fault - my take is that Dess is fully dead, or believed to be. There was huge fallout from this, since it seems to have screwed up the relationship between the Holidays and the Dreemurrs a bit - they still interact just fine, but they have a lot of emotional baggage weighing it all down. I figure that Mayor Holiday, Toriel, and Asgore each blame Asgore for Dess's death, while Rudy doesn't blame Asgore. And the blame Toriel and Asgore place on Asgore leads them to split, her because she can't stand to look at him and know that his screwup led to the death of a child, which could have been one of their children just as easily, and Asgore sort of accepting it as part of his life falling apart because he figured he deserved all of that.
I think Asriel might be angry at both Toriel and Asgore for how they dealt with that. While Dess was probably close to Asriel, and he probably cared a lot about her, worrying about whose fault her death was didn't bring her back. In fact, all it did was isolate Kris, between the fact that the kids didn't hang out all together anymore and they don't seem to be encouraged to visit Asgore, though they're allowed to. It also ruined the normal routines and family interactions they used to have. So Asriel took up the slack of that, taking Kris to get hot chocolate and being their friend through all of this. But, at the same time, having all that on his shoulders and having the expectations of a small town who knew him his whole life, it's no wonder he went off to college. He probably didn't want to live his life the way everyone else expected him to.
I think the setup that he's the golden child who wins awards and is beloved by all is setting that up. People view him a specific way, and it's a kind of pressure - he's the dependable one, the good kid, the good influence. He's the town's best example of the next generation. He's been through a lot but he's never wavered. And I think that's hard for a person to keep up with.
For that last reason, I suspect when we do see Asriel again, he'll have done something that surprises everyone but Kris. Maybe a relationship, or a life choice or something that his family wouldn't approve of, showing that there's an emotional barrier between him and his parents that he didn't feel comfortable enough to share something about himself with them (though of course Kris knew about it). I doubt he's the knight purely for proximity reasons (he's not there). But it could be that his actions are related to it anyway, like if he taught Kris how to open dark fountains. But I think there will be something else, unrelated to all of that, that everyone will be grappling with because he's finally broken the mold of their expectations in some way.
And kind of unrelated to all that I think of UT!Asriel and DR!Asriel as completely different people in a lot of ways. So I headcanon UT!Asriel as aceallo, but DR!Asriel as aroallo. Based on not a lot but that's my headcanon
