Place cool water into a medium-sized saucepan.
Sprinkle agar agar powder over the cool water and let it absorb for 5 minutes.
Heat the agar mixture until it simmers and cook for 2-3 minutes stirring constantly with a spatula.
Sprinkle in the sugar and continue cooking for another 2-3 minutes until the liquid becomes clear.
Remove from the heat and mix in candy flavoring.
Lightly grease a heatproof glass dish with coconut oil or vegetable oil. Pour the mixture into the glass dish.
For gel food coloring, put some gel food coloring on a toothpick and run it through the mixture to make marbling. Repeat with one color or with multiple colors to your liking. For liquid food coloring, put a few drops on top and swirl with a toothpick. You can blend fully or leave it marbled.
Place the container into the refrigerator for 2-3 hours until set.
Remove the set jelly from the container and cut into crystal shapes using a sharp knife.
Place the crystal jellies onto a parchment covered cookie sheet and loosely cover the jellies with plastic wrap to avoid dusts. Let them dry at room temperature for 2-3 days until a hard crust forms on the outside. Enjoy!