Tonic

Location
Tonic is located in Lunpa Fortress, in a room connected to Donpa's bedroom that is inaccessible the first time you sneak into and complete the optional dungeon. After defeating Toadonpa and letting Hammet be brought back to Kalay, you are allowed to sneak back into Lunpa Fortress. Make your way all the way back to Donpa's bedroom again, and in a cutscene Donpa will thank you for your help and let you enter a room to collect Tonic, which he claims is a creature he "fought once long ago" - not likely, since the Djinn were only released into the world for the first time at the beginning of the game.

Description
When Set, it increases base HP by 8, base PP by 3, base Defense by 2, and base Luck by 2.

When Tonic's battle effect is used, all status ailments from all current battling Adepts are removed, including the likes of haunt. Its effect is identical to that of the TLA Venus Djinni Salt.

Ability analysis
In Golden Sun, Tonic is the one effect that matches the classic "Remedy" effect present in many RPGs, healing both conditions that would disappear at the end of the battle (e.g. Stun, Delusion) and effects that have to be manually removed (e.g. Venom, Haunt). It can be a very useful effect for a designated healer and supporter like Mia to use, particularly if multiple Adepts are afflicted with multiple conditions. It is not worth using it to remove one Adept's Poison or Venom condition, which can be removed by a simple Cure Poison Psynergy, though.

In The Lost Age, when Isaac's party joins Felix's party along with their returning Djinn (granted that Password data transfer is in effect), Tonic's battle ability makes it a second Salt, a Venus Djinni acquirable in Contigo as soon as that game's party enters the Great Western Sea. The two are equally usable for whenever a particularly widespread status condition situation transpires, though in a way they are limited because those sorts of situations do not occur often; the only real beneficial use for them is when multiple Adepts are afflicted with Haunt and Death Curse in the fights against Doom Dragon and Dullahan.

Name Orgin
A tonic is a drink intended to restore or invigorate, hence the reason the Djinni Tonic cures status conditions.