Rock candy is an item found in EarthBound and its rerelease in Mother 1+2. When eaten, it gives a permanent increase of 1 to one of the character's stats at random.
There is a glitch in EarthBound (removed in Mother 1+2) where the Rock candy can be used multiple times. To do so, one of Ness' party has to have at least one condiment, and a Rock candy in the last spot in their inventory. Entering a battle and using the Rock candy on anyone results in the Rock candy remaining and only the condiment being used. Both Sugar and a Jar of Delisauce double the regular effect and are therefore the best to use in the glitch. However, be careful with this glitch, as adding anything to a statistic of 255 will result in it being reset down to 0, and odd effects have been noted with having an HP or PP stat increase past 999.
The best way to get incredible stats is to have one use the Rock candy multiple times in battle. The more Sugar Packets, the better the stats. This trick works especially well before a level-up. It is also possible to set up more than one Rock candy to gain more stats in a single level-up.
Named after the Rock candy item, some fans of the Mother series made six albums of music as a tribute to the series. Their music can be found here.