Petra

Petra is a Venus Djinni found in Golden Sun: The Lost Age.

Petra is the seventh Venus Djinni in Golden Sun: The Lost Age. The separate Djinn list viewable with the Select button from the status screen lists Petra and all other Venus Djinn introduced in The Lost Age before the seven Venus Djinn from the original Golden Sun, most likely because all the Djinn from the original game can be gotten all at once late in The Lost Age. However, the original Djinn are ordered before all of the Djin introduced in The Lost Age in the Djinn inventory screen while they are allocated to characters. By this order, Petra is the fourteenth Venus Djinni in the GBA series, rather than the seventh.

Basic description

 * "Turn a foe to stone."

When Set, Petra increases its Adept's base HP by 11 and base Defense by 3.

When Petra is unleashed in battle, the user produces an effect that prevents the next one action that the target has not performed yet this turn from executing. If an enemy only has one action per turn, it will essentially be prevented from doing anything this turn, while an enemy that acts twice per turn will only act once. This effect has the "strikes first" property, meaning it will be the first performed action  in a given turn regardless  of the agility rating of the user and any  other combatant in battle.

In The Lost Age, Petra's unleash animation visually resembles the user summoning a glowing image of a Venus Djinni that hovers above the party and generates a mass of glowing yellow fog at the targeted enemy, and for a moment the target stops animating and turns monochrome to indicate "petrification".

Location
Golden Sun: The Lost Age: Petra is a Djinni that is randomly encountered in a specific area of the overworld that otherwise appears to be pointless scenery. Thus, it is very often missed by players playing the game the first time without any outside information. The battle with Petra may ensue in place of a random battle in the pictured area in northeast Hesperia in a vertical "V"-shaped stretch of forest; this region is most easily reached by sailing the ship into the river opening on the northeastern tip of the landmass. Petra then must be battled to be acquired.

As an opponent (The Lost Age)
Statistically, Petra has 830 HP, 77 PP, 260 Attack, 79 Defense, 227 Agility, and 26 Luck. Like all other Venus Djinn that are fought, in terms of resistance, it has a Venus Resistance rating of 193, Mercury and Mars Resistance ratings of 100 each, and a Jupiter Resistance rating of 25, and in regards to its abilities it uses its available Venus-based attacks with a Venus power rating of 125.

Petra can use the following battle commands:
 * Stone Spire: Used 53 out of 256 times, this is a Psynergy spell that causes five large stalactite to fall down from above onto the party and shatter, dealing a Venus-based attack with a power rating of 160 and a range of 3. This ability consumes 22 of its user's PP.
 * Briar: Used 47 out of 256 times, this is a Psynergy Spell that generates a mass of thorny spiked vines at the position of the party of Adepts, dealing a Venus-based attack with a power rating of 70 and a range of 3. It costs the user 11 PP.
 * Wild Growth: Used 41 out of 256 times, this is a Psynergy spell that causes a large amount of thorny vines to erupt from the ground and though the party, dealing a Venus-based attack with a power rating of 110 and a range of 5. It consumes 19 of the user's PP.
 * Mother Gaia: Used 35 out of 256 times, this is a Psynergy spell that causes the ground beneath the enemy to open up and engulf the party in a wider reverse shower of Venus energy and medium-sized boulders, dealing a Venus-based attack with a power rating of 100 and a range of 5. This ability consumes 17 of its user's PP.
 * Quake Sphere: Used 29 out of 256 yimes, this is a Psynergy spell that prompts three rectangular sections of ground underneath the party to jolt upward and retract into the ground quickly thrice in succession, bouncing each Adept three times, dealing a Veus-based attack with a power rating of 65 and a range of 7. This ability consumes 15 of its user's PP.
 * Attack: Used 28 out of 256 times, this is this monster's standard physical attack, but for this monster it is counted as a Venus-based attack rather than a non-elemental attack.
 * Flee: Used 23 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.

When defeated, Petra yields 937 EXP and 631 Coins, and the Petra Djinni is added to your party's Djinn collection. If you fell it with an offensive Jupiter Djinni like Wheeze, its rewards increase to 1218 EXP and 820 Coins.

Very easy to destroy in one turn with summons like Thor, which you really should have considering this is found in the Great Western Sea segment of the overworld much later in the game.

Analysis
General: Petra is one of several Djinn that can either nullify an enemy's action entirely or prevent one of a boss' multiple actions in a given turn. This can be potentially very useful, and specific applications are possible when this Djinni is combined with the other Djinn that has the same effect (so that even a boss' multiple  actions can be negated in a turn). The equivalents to Petra in Dark Dawn are the Venus Djinni Ivy and the Jupiter Djinni Doldrum.

By game
Golden Sun: The Lost  Age: Petra can be found as soon as the Great Western Sea is entered. Therefore, it can be used to nullify one of the potentially powerful actions of the boss encounters before Isaac's party joins - Moapa and the two Knights at the end of Trial Road, and then Karst and Agatio at Jupiter Lighthouse. When Isaac's party joins Felix's party along with their returning  Djinn (granted that Password data transfer is in effect), they bring an identical equivalent to Petra, the Venus Djinni Ground. Both Ground and Petra together are equally usable. One particularly great use of Ground or Petra is in the third and final stage of the final boss fight against Doom Dragon; the two moves Doom Dragon is allowed to use will almost always both be extremely powerful and deadly, so preventing one of them will be a huge help in surviving the end of the battle.

Another especially under-appreciated use of this effect manifests in the start of the Star Magician battle; Ground  and Petra sharing the same priority as the Guard Aura monster skill the  Guardian Ball uses to  make the Star Magician invulnerable with  means that if the user of  Ground/Petra has higher Agility than the  Guardian Ball (though the  Guardian Ball has one of the highest agility  ratings in the game, with  292 agility; this problem can be solved  beforehand with  Vine/Mud), the user can outspeed the Guardian  Ball and make it  unable to use Guard Aura with Ground/Petra, thus  ensuring that the other  three Adepts this turn can fully and safely make use of the strongest summons all together. This Djinni can singlehandedly make a very tricky  and challenging optional boss battle  much more simple than otherwise possible, in other words.

When you have both Djinn in your collection, the two together can completely prevent any enemy that only acts once per turn from ever  attacking. While Adept One uses one of the two Djinn to freeze the enemy, Adept Two re-Sets the other of the two Djinn that was used to freeze the enemy in the previous turn, and  the next turn Adept Two does  the freezing while Adept One resets his  Djinni. Adepts Three and Four, in the meantime, are the fighters who safely deal damage. This alternating strategy can be infinitely performed to ensure complete  safety for the Adepts throughout the battle  (though of course the battle would be a lot longer and more tedious this way). This is not as insanely helpful against any boss that can act more than one turn, though, since its second attack will not be prevented - and the reason this strategy never caught on is that none of the bosses following the reunion act only once per turn to begin with.

Name Origin
Petra is an abbreviation of the word petrified, which refers to any organic material that is changed to stone (hence the reason the Djinni Petra causes targets to become immobile). The most common case of this is petrified wood.

Interestingly, Petra is also the Greek word for rock. There is yet another Petra, this one an ancient city carved out of the cliffs in Jordan.