Press Z to look at things. Use the arrow keys to move around. Everything else will be taught as you go. There are some secrets not in the original, and some glitches too.
Coding done by me All other credits to Toby_fox After you fight the dummy, the demo ends. I will not be working on this anymore, so go check out some of my other projects! If you're looking for an actual Undertale battle, I made one here: https://scratch.mit.edu/projects/906573543/