Delish.com came out with a list of candy-related Halloween pranks you can pull on people. You probs shouldn't use any of these on trick-or-treaters because of allergies, but some of these would be really fun to prank your friends with.
1. Make candy apples, but use onions. You can't tell the difference until you bite into it. (GROSS!!)
2. Put out a bowl of M&M's mixed with Skittles and Reese's Pieces.
3. Make a small hole in a Reese's Peanut Butter Cup , take out some of the filling, and replace it with mustard or Sriracha or something equally gross.
4. Unwrap a few yellow Starburst, and replace the candy with cheese. Juuust make sure they eat it right away. Nobody wants stinky cheese cleverly disguised as a Starburst lying around.
5. Take a box of something like Nerds or Sour Patch Kids, swap out the candy for a few fake bugs and then glue it shut.
Get even MORE pranks HERE.