Corona

Location
Corona is the first Djinni players can come across in Golden Sun that is randomly encountered in a specific area of the overworld that otherwise appears to be pointless scenery. Thus, it is almost always missed by players playing the game the first time without any outside information. The battle with Corona may ensue in place of a random battle at the end of a vertical stretch of land parallel to the Mogall Forest region in Angara, in the pictured "island" north of Xian, and Corona then, of course, must be battled to be acquired.

As an opponent
Statistically, Corona has 355 HP, 24 PP, 144 Attack, 41 Defense, 76 Agility, and 8 Luck. Like all other Mars Djinn that are fought, in terms of resistance, it has a Mars Resistance rating of 193, Venus and Jupiter Resistance ratings of 100 each, and a Mercury Resistance rating of 25, and in regards to its abilities it uses its available Mars-based attacks with a Mars power rating of 125.

Corona can use the following battle commands:
 * Flare Wall: Used 53 out of 256 times, this is a Psynergy spell that causes two patches of fire stacked on top of each other to go through multiple Adepts and deal a Mars-based attack with a power rating of 40 and a range of 3. This ability consumes 7 of its user's PP.
 * Volcano: Used 47 out of 256 times, this is a Psynergy spell that causes a fiery pillar to explode at the targeted Adept's position, dealing a Mars-based attack with a power rating of 45. This ability consumes 6 of its user's PP.
 * Mad Blast: Used 41 out of 256 times, this is a Psynergy spell that causes a moderately large explosion of vaguely liquid-ish fire to combust at the enemy's general position, dealing a Mars-based attack with a power rating of 50 and a range of 3. This ability consumes 9 of its user's PP.
 * Attack: Used 40 out of 256 times, this is this monster's standard physical attack, but for this monster it is counted as a Mars-based attack rather than a non-elemental attack.
 * Fireball: Used 35 out of 256 times, this is a Psynergy spell that projects a moderately large amount of fiery spheres that arc over and into the party's position, dealing a Mars-based attack with a power rating of 65 and a range of 5. This ability consumes 12 of its user's PP.
 * Nova: Used 29 out of 256 times, this is a Psynergy spell that causes a large explosion of fire to discharge at the party's position, dealing a Mars-based attack with a power rating of 70 and a range of 5. This ability consumes 13 of its user's PP.
 * Flee: Used 11 out of 256 times, this enemy has the ability to attempt to Flee the battle, thereby ending the battle if successful without rewarding you with the associated EXP, Coins, and the Djinni itself. Since this is a randomly battled overworld Djinni, however, it can be very quickly fought again just by running around in the same area you first fought it in.

When defeated, Corona yields 173 EXP and 210 Coins, and the Corona Djinni is added to your party's Djinn collection. If you fell it with an offensive Mercury Djinni like Mist, its rewards increase to 224 EXP and 273 Coins.

When the game is played perfectly, you have three of each other element of Djinni by this point, so you should by all means try to destroy Corona in one turn with Cybele, Procne, and Neptune, the last of which should deal over 200 damage in one hit. Even if not, Corona's chance to flee is lower than other Djinn that are fought to be earned.

Description
When Set, it increases base HP by 12, base PP by 3, base Defense by 3, and base Luck by 1.

When Corona's battle effect is used, all currently active and alive Adepts get buffed with a 25% temporary increase to their respective defense ratings. This effect is identical to the battle ability of the Venus Djinni Iron shortly into The Lost Age, and is twice as strong as the battle result of the Protect/Protector Psynergy (and is also attached to a Djinni rather than to the user's PP meter). Another easy way to remember this Djinni is that it is the defense-based version of the attack-based Forge Djinni gotten earlier.

Ability analysis
In Golden Sun, Corona is the one Djinni that is Protect doubled in effectiveness, and can be a very valuable battle effect to players who incorporate buffing all party members' physical defense ratings in their battling approaches. When the game is played with all Adepts in their respective mono-elemental class series, both the Guard Psynergy series and this Djinni are present on Garet, so it could be said that this is a superior option for Garet to make use of if you have that choice. Technically, this Djinni only gets better as the game progresses and party members' attack ratings increase. Note that defense-buffing effects like these stack with each other up until all Adepts have +50% defense rating modifiers.

In The Lost Age, when Isaac's party joins Felix's party along with their returning Djinn, Corona's ability makes it a second Iron, a Venus Djinni with the exact same effect that the TLA party finds very early on in that game, and these two together are the only Djinn whose effects are two Protects worth of attack buffing at once. Whether you find it useful for Adepts, with or without Protect, to have one or both of these Djinn Set onto them ready for them to use is entirely up to you and whatever battling approach you deem worthy, though.

Name Origin
A corona is the high-altitude gaseous envelope of the sun that we can see during a solar eclipse as the golden ring around the blocked out sun. A fever is a symptom where the body's internal temperature rises above normal. Note that the English translation of the games switched the names of the second and third Mars Djinn.