You know what? Me too.

Bumping noses is totally a kiss in monster society. Believe me, I know these things.

The lost souls had their items swapped in our version of Underswap, but they still retain their aspect and that hugely influence the way those items are used. 

You have actually seen them before. They are swapped with the Drakes, who you have already seen in the GIftmass comic.

And you have seen Dogami too, doing his job as announcer in this comic.

But I guess you haven't seen Dogaressa yet uh...

“Pfft, good luck. Try all you want, but you can’t hurt me. You have no power here. I’ve been alive longer than your ancestry, I know how these things work. And in here? You’re a joke.” 

Bun is the one that will tell you about the delta rune and prophecy. She’s the queen of knowing all the gossip in the underground, even though shes retired, so she will give you some of that as well. Bun also will tell you about the silly skeletons running around Snowdin. 

She’s also the one who stays in her shop during the genocide route. She wants to stall as long as she can to allow others more time to get to safety. Plus, she’s dealt with worse humans anyway. She isn’t afraid.  

Gerson leaves a note, asking for no harm to come to the kids he takes care of and friends. He might give some gossip too when monsters aren’t being murdered, but mostly about Waterfall and Alphys. 

As for what each of them sells, they both sell the same items they respectively sell in game. It’s just their roles and most of the info they tell you that is switched.  

In the way a terrorist differs from a radical environmentalist. Both are extremist that can go through immensurable and at time horrible lenghts to achieve their goal, but that goal is completely different. While canon Chara wants to erase the world whose existence they consider pointless, what Swap!Frisk seeks is to actually manipulate it to make it worth of salvation. The world needs to change if it is to be saved, and no sacrifice is too big to ensure that.

And well, there is also the thing about Chara feeling no remorse. Frisk does feel remorse, and a LOT of it, but they are convinced the end justify the means.