Alright. Today I'm going to be showing you guys how to get any item in Undertale!
So go ahead and watch the video. If you can't for some reason, I'll give a quick rundown.
1. Open RUN and enter %localappdata%, click UNDERTALE.
2. Open file0 with notepad.
3. We are going to be changing every other line between 13 and 27. They correspond with the various slots in your inventory. So 13, 15, 17 etc.
4. Find the item id's of the items you want here: http://rawr.ws/undertale/items
5. Fill out the lines with the corresponding lines in file0.
6. Save, and you're done! If you have any trouble, comment on the video.