Magical jelly can be brewed with the Cauldron in Candy Box. It can be used during quests, and functions like a bomb. It drops behind the player when used, so Teleport scrolls may be needed so the enemies can reach it.
To make Jelly, add 600 candies to the Cauldron and boil (you can let the water boil or burn) them. Then click "stop" and add 6,000 lollipops and mix them for ten seconds. Click "stop", then again add 600 candies, boil them, and click "stop". Then put them into a bottle(s).