Vorish head cannons with Deltarune/Undertale characters?
Absolutely! I'm gonna throw in U.ndertale Yellow characters, too, for free! (Doesn't include the new D.eltarune guys, still spinning them in my head and figuring them out so also no spoilers to worry over).
UT!A.sgore D.reemurr: I guess he gets two descriptions since he's very different in both canons. UT!A.sgore I think gets lots of willing prey, mostly guards or other citizens that wish to show their immense love for their king by being his lunch--this flusters him too much to ever deny. He also really enjoys humans--in a post-pacifist scenario, this is usually a guilty pleasure or something he likes to keep private because it's a bit embarrassing. While I don't think he's strictly willing prey under normal circumstances, he will usually gives up/accept his fate after a point--either by getting defeated in battle or realizing he can't get free from his predator's gut. I also like to think he's someone that lots of people wanna eat but won't usually go for and he's too oblivious to really notice.
DR!A.sgore D.reemurr: Himbo DILF. Feels like that's self-explanatory. Tends to do lots of accidental/unaware vore/digestion, misunderstandings that end with his belly full, or 'eat a guy' is just the first thing that comes to mind when he needs a solution to a problem and he just rolls with it. I also like to think this version of Asgore really likes to eat college-aged guys and that's the thing he's kinda flustered by given his college-aged son. Similar to UTA.sgore, I think lots of people wanna eat him and he's too oblivious to notice it. Difference here being that he's not a king and people will be less likely to hold off, and he leans a lot more into the unwilling prey side of things. But since he's not a powerful boss monster he's also a lot easier to take down if someone tries. Though he can also be convinced into being food if someone finds the right logic.
A.sriel D.reemurr: Look, A.sriel's a giant dork, this guy's going to get teased and flustered more than anything. He can absolutely eat people--enough booze or social peer pressure can generally convince him to do a lot. He wants to be a cool frat guy at college so he'll do really stupid and poorly-thought-out things to achieve those goals. I also like the idea of him being a roommate grinder though, burns through them like crazy cause he can't help himself. But he's also just easy prey--he's kinda scrawny, easily flustered and tricked, and overall not difficult to get down. Definitely unwilling prey most of the time but results may vary. But more than that I think he just gets teased a lot by the other predators in his life because he's just that easy to mess with. And who could resist doing that?
S.ans: You would think a guy this lazy wouldn't be much of a predator...well, I don't care about that. He finds his ways to get his meals. Blue magic is pretty useful for quickly throwing someone into his maw by only lifting a finger. Or even less work--he just opens his jaws up wide and has some nearby meals do all the work for him. Somehow this keeps him well-fed. And I honestly like to write him with a meaner streak--just very casual in his regard of other people as food and making jokes about their plight without much care. As for being prey...well, trying to fight back is a loooot of work, so he tends to just not do that. This makes him an easy meal but who would want to eat a bunch of bones for lunch? Probably more people than Sans really anticipated. Ah well.
P.apyrus: Also very big on unaware/accidental vore/digestion. Like, if someone ends up digesting while he's trying to detain them or some training goes wrong or he misunderstands someone's question as offering to be lunch...no real harm done, right? After all, people should be excited to be a nice meal for the Great P.apyrus! Of course, if he can also justify the logic to himself as being for the greater good, that works, too. As for being prey, it's definitely an escalation of panic. P.apyrus is fairly confident that he either won't be harmed or will get out and the longer he lasts the harder it gets to keep believing that. Though, by the time he actually does attempt to get out...it'd be a little too late.
G.rillby: He's not a very expressive person so people tend to mistake that as "not a danger". And to well-paying customers (and Sans, I guess) this is generally true. But rowdy, unpaying, or rude customers tend to find very quickly that G.rillby is not a pushover and has a very low tolerance for these things. Of course, with his gut often obscured behind the bar, it's still easy for people to miss this even if he's currently processing a customer. Staying after closing is another no-go and it's not uncommon for him to be cleaning up the bar while some knocked-out drunkards are sloshing around as an easy dinner. Of course, being the guy in charge of the place, Grillby is rarely prepared for someone to try and turn him into bar food so he's easy to catch off guard. Especially if he's being dragged over the bar. He might give some indigestion or heartburn, especially if he's squirming, but he's a very warm and soothing meal as well. So it's worth it.
R.G01 & R.G02: They get to be put together because they do everything together and share a braincell. Very often they're in situations where one eats and the other is tending to their gut. Sure, they might get meals together sometimes, but once one of them has a full gut the other one loses the braincell they share and can only focus on belly rubs. This works out for them though. They're probably not very good influences on each other, either, since they also wanna show off to the other. It makes them good guards, if indiscriminately eating people makes you a good guard. If one of them gets eaten, though, the other is almost certainly going to follow. Mostly in some romantic attempt to free them that just ends with both guards stuck in their predator's gut. They're honestly much easier to handle together even if it's twice the meat since they won't be thrashing nearly as hard. Two for one deal!
S.watch: He's very prim and proper so he does make an honest effort not to eat out in the open. Though he does snack on S.watchlings that make mistakes or customers who ask him for certain 'services'. He might also just eat someone really quickly for his lunchbreak if that's more efficient. But he does try not to have a full stomach while working since it's not very polite...so it keeps him very flustered if it does happen. Now, he'll be very displeased at the idea of being eaten--it's rather gross and unbecoming--but he's also not going to make a huge fuss over it...if it can be helped. Customers or other people who ask politely can generally get him down with little complaint, though he may become more upset over time. People who get him by surprise or while he's working are going to get a very fussy butler, but that doesn't mean he won't go down smoothly.
S.watchlings: For a bunch of big, buff butlers they're kinda...doofuses. Pretty easy to tell why S.watch is in charge. S.watchlings eating one another for whatever reason is a fairly common occurrence, so seeing a few butlers walking around with full guts is expected. Does this get in the way of their work? Yes, constantly. Gives more excuses for eating each other. This means they're also very good as prey, given their training, and most anyone can eat them without too much issue. It does make worker retention a bit difficult but nothing that S.watch can't handle.
R.udy Holiday: Sick old man lying in bed all the time...he still manages to eat people with the benefit that no one ever sees it coming. Visitors and hospital staff likely disappear with him a lot but, hey, he needs to eat a lot so he can get better, right? The exchange rate of his own health vs. all the people he eats might not be the most evenly weighted but that's not a problem, is it? He also likes to crack jokes too often and they're about as bad and mean-spirited as the other comedian in the cast's. Though, the thing that makes him a predator no one suspects also makes him a rather easy meal. Sure, that might be a little cruel, eating a sick guy at the hospital--but it's gotta be better than what they serve in the cafeteria, right? R.udy might even suggest it to someone that's particularly close to him himself.
S.tarlo: Being a sheriff can be dirty work, but someone's gotta do it. That tends to imply detaining criminals in his stomach or the injured for transport or to just kick some people that had too much to drink out of the local watering hole. Is there still someone left to let out by the time he gets to where he's going? Maybe not, but that's just how it is in the Wild East--least, that's what S.tarlo tells himself after another 'accident' occurred. Though, with how popular and beloved he is in town, he might have a few fans that want to take a ride in the sheriff's personal cell...if there's nothing left to let out later that's probably what they wanted, right? S.tarlo has terrible control of his stomach so this is a constant problem with him. He's never really ready for real danger, though, so if someone actually wants to get the sheriff out of the way...they'll find that he goes down a lot easier than expected. Kicking and screaming, sure, but still easy. He's not even that rough on the stomach despite how much he might try. Who appointed this guy as sheriff again?
D.alv: Quiet, socially awkward guy that lives alone means surprise visitors get eaten. It's a strange shock reaction to have but maybe that's why D.alv stays on his own. Either way, he at least has a captive audience to talk to for the foreseeable future. They might not listen to anything he says and keep interrupting him with muffled complaints and moving around but it's better than nothing, isn't it? It's always sad when they eventually have to go but it's also D.alv's favorite part--not that he'd openly admit it. Though he's also an easy meal because of this. Get him by surprise and there's not much he can do. He won't fight back very hard and just try to convince whoever ate him to let him go...it probably won't work but it's the only option he has. And since no one really knows he lives all the way in the ruins, no one's even going to notice if he's gone. Ah well, the price for privacy.
M.o: Money talks and it can get him to do a lot of things. What he will do even without a price is eat someone--a business tycoon like himself needs to stay full and have lots of energy, and this is a very cost-effective way of getting that! Might be able to convince him not to with your wallet but it really depends on how hungry he is. Non-paying customers will always be his go-to, though. A lot of his random schemes and business ideas seem to end with him getting rather full as well, even when it wasn't planned that way. But he can also be convinced to be someone's snack for enough money. Is that money going to be very useful once he's churning down? Maybe not but that's just business, baby!
El B.ailador: He needs lots of energy for dancing, right? Gulping a guy down definitely gives him plenty of energy to work with while he dances his heart out. Makes for a very sloshy and gassy dance routine but that's not so much of a problem, is it? It gets his prey 'dancing' plenty too from how hard they kick and shift around but they never can keep up with El B.ailador. Though, he's definitely a target himself--mostly by people who just think he's kind of annoying. Not everyone appreciates surprise dance-offs or loud music. Easier to just eat the guy and be done with it. He's a real good squirmer though and might give the average person a stomachache.