It's a fairly good story. I'm disappointed that there isn't more (perhaps I should make one).
Things you do need to work on are grammar, spelling, and punching spell check in the face. It's being an idiot. Barrier got turned into barrel, which implies that Frisk punched a barrel and it broke.
...hey, that would actually make a pretty good story...
Uh, anyway...I would recommend reading Farla's guide on grammar, or just reading an online manual or something. You should also space out your paragraphs a bit more.
Other than those things, this is a great story!

I guess the serpent wanted to have a bad time and Daphne Blake probably would've did the fighting her self if she saw one of friends in danger samething for a kid if she didn't see sans doing it for her.

You said that frisk "broke the barrel" instead of the barrier...yes...a barrel kept them all trapped underground

I love it! I love it soooo much! There should be more Scooby Doo and Undertale crossovers. That Jerry dude is an idiot *shook head* his issue really needs to be resolved or something.

Great job !

Should be more Scooby Doo/ Undertale cross overs. I wonder what would happen if the Skeleton Bothers seen Shaggy and Scooby making a two story sandwich made up from everything, including spaghetti and ketchup.

The guy did it just because he hated the park? That is low for him. Guessing Scooby will see skeletons in a new light, since Sans saved him and Frisk from the Serpent.

That snake won't get away with this. Did you get the idea for the Park Serpent from the Demon Snake?

Two skeletons are in deep trouble today

The Park Serpent's dead with Sans coming to the rescue

I thought Shaggy and Scooby would have met Sans at the hotdog stand. Would be a little awkward for Shaggy and Scooby sense the Skeleton Bros would bring memories about the Skeleton Men, and Sans would just shrug at the two

I love the story so far is great

I love it! I know you buzy, but I just wanted to say that I LOVE THIS FANFICTION!