Fizz

Location
Fizz is a Djinni that is automatically handed to you as you play through the game, being present on Mia as soon as she joins your party in Mercury Lighthouse somewhat early on in Golden Sun. Aside from Flint, Fizz is the only Djinni in the game that is impossible not to obtain.

Description
When Set, it increases base HP by 9, base PP by 4, and base Defense by 3.

When Fizz's battle effect is used, a targeted Adept on the player's side has their HP cured by an amount equal to 60% of their maximum HP. It is nearly identical to the Mercury Djinni Spring in The Lost Age, only with that restoring 70% of maximum HP.

Ability analysis
In Golden Sun, while appearing to be easily understandable and practical as a battle option, particularly coming from a designated healer such as Mia, it is not very useful as an ability in practice because of the abundance of easier-to-use and more direct healing items and Psynergy available. And while it's technically one of the only effects available to the party that cures HP based on maximum HP meter - thus making it technically better over the course of the game as the Adepts gain more HP - the items and Psynergy become better and more practical as well. There will be cases where using it will not cure as much as a simple usage of a Psynergy from the Ply Psynergy series, and the fact it saves PP that would have been spent on Ply spells otherwise does not seem enough of an advantage to make up for it.

In The Lost Age, when Isaac's party joins Felix's party along with their returning Djinn, Fizz' battle effect is even less noteworthy because the Mercury Djinni Spring, which is automatically acquired when Piers joins in that game a long time beforehand, recovers HP by an amount equal to 70% of the target's maximum HP - and that Djinni itself is not considered so practical because of the more straightforward healing options available in various forms.

Name Origin
"Fizz" is the bubbles in carbonated water. The Mercury element is associated with water.