The Purple Chu Jelly can either damage you or it can heal you a couple hearts. The Red Chu Jelly heals 8 Hearts. The Blue Chu Jelly heals all your hearts. The Rare Chu Jelly(Found in the Cave of Ordeals and around the Snowpeak area) heals all of your hearts and boosts your attack power until you take damage. The Yellow Chu Jelly works the same way as Lantern Oil.

Believe me, I'm an expert, as my name suggests.

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Good ol' Chu Chus, supplying ZU with just what it needs: CHU JELLY!