Poseidon

Poseidon (ポセイドン Poseidon) is a mythical figure in Weyard’s past and serves as a boss in Golden Sun: The Lost Age. Among boss monsters he serves a notable influence upon plot progression. He resembles the classic image of King Triton.

In Golden Sun: The Lost Age
Poseidon blocks the way into Lemuria and ensures that you cannot enter the city until you have thoroughly explored and completed the entire Great Eastern Sea; otherwise, the city would be accessible as soon as the Lemurian Ship is first acquired. The means by which Poseidon achieves this is that, in battle, no attack whatsoever can damage him because of an impenetrable force field that guards him. Only using the completed Trident of Ankohl as an item can remove the force field of Poseidon, after which it becomes a normal boss battle that can be completed. The Trident can only be completed through thorough journeying and event completion around the Great Eastern Sea. (On a related note, Poseidon can be encountered in the Monster Battle Mode, but fortunately he does not possess this invincibility.)

Poseidon's threat value as an adversary primarily derives from his Watery Grave ability, which not only deals a fair amount of damage to the entire party, but can instantly down any number of the four Adepts for no reason other than chance. Also of note is his Counter-rush - if he were to use it on a turn in which all four Adepts attack or do anything else to him, all four of them will end up physically struck, in addition to whatever is his "normal second move" he would perform that turn.

Jenna learns Serpent Fume at level 26, so training the party to that level may make this battle easier. Also, if all six possible Venus Djinn have been obtained at this point in the story, Felix can use the immensely powerful Odyssey in battle, the only disadvantage being that it doesn't capitalize on Poseidon's weakness to Mars-based attacks. Other ways to take advantage of this weakness would be to utilize the Pierrot's Juggle (Mars-based) abilities, or redistributing one or two Mars Djinn to each character, which may permit some unique strategies.

By this point in the game, the player can have the first twenty-four Djinn available, six of each element, meaning a variety of options are available. Most efficient may be to put one Djinn of each element On Standby, allowing for two Barbarians and two Savants - have the Brutes spam Planet Diver against Poseidon, while the Savants heal using Wish Well as necessary or attack with Plasma or their physical attacks. Another option is to use four tri-elemental classes, which allows for a more diverse strategy. Ultimately, victory in this fight is a matter of patience and care - make sure nobody's HP goes too low, and Poseidon will go down eventually.

Poseidon is especially likely to be affected by HP-draining effects. It has the following statistics:

Poseidon acts twice per turn and draws from two separate command lists, always calling a move from the first list and a move from the second list in that order for the turn. For the first list, it proceeds through the command list in sequential order with a random start point; this means that any one of the eight actions listed below can be the "starting point," and the next turn's action will be the one listed beneath what had been used, cycling back to the top of the list when the bottom of the list is reached. It uses all of the following battle commands from both lists with :

Background and Story
Poseidon is an entity that has long slumbered within the depths of the Sea of Time, near Lemuria. According to NPCs in The Lost Age, Poseidon was once the "true rightful king of the seas" far in the past (perhaps Weyard's ancient past), and is apparently the "Sea God" that the Shrine of the Sea God in Indra is dedicated to. Further details to Poseidon's apparently important role in Weyard's ancient history are not provided. By the present age, he has become a mindless monster that would cause terror if he wakes up.

At the end of Golden Sun and the beginning of The Lost Age, Mercury Lighthouse and Venus Lighthouse have been lit. This is what causes Poseidon to awaken, and he in turn generates the large tidal wave at the start of the second game, the one that indirectly drives Piers out of Lemuria. As The Lost Age progresses, Poseidon is the reason why Felix and Piers are not able to enter Lemuria until much later in their journey across Weyard, when they have achieved the reconstruction of the legendary weapon, the Trident of Ankohl, needed to do combat with Poseidon properly.

Poseidon is eventually defeated by Felix's party when they attempt to sail into Lemuria, with the Trident of Ankohl in tow. Using the weapon, they break apart Poseidon's aura of invulnerability, and proceed to engage in a fierce battle until Poseidon is destroyed.

The the battle against Poseidon would become well-known in the 30 years following the Golden Sun event. By the time of Dark Dawn, a wooden replica of Poseidon appears as a obstacle in the Psynergy Training Grounds, a theme park representative of the exploits of the Adepts, now referred to as the Warriors of Vale. The replica consists of three wooden panels, showing Poseidon's head and fists, and each must be burned using Fireball to continue. However, "Poseidon" is blocked by three geysers of water, representative of the force field. To remove the force field Matthew and his party must complete a series of three puzzles, which represent the three pieces of the trident. Once completed, the geysers disappear, allowing Matthew and his party to continue on.

Trivia

 * In Battle Mode, if the player uses Mold on him while he uses Counter-rush, he will take damage, then attack himself due to Mold's effect.

Cultural references
Origin: Greece

In Greek mythology, Poseidon was the King of the Sea and one of the original 6 gods and goddesses in the Greek Pantheon. He was commonly depicted as carrying a trident, which the game provides a sense of irony for, as the tool that ultimately leads to his downfall is the trident. Poseidon was the brother of Zeus and Hades in Greek mythology. Poseidon was referred to as Neptune in Roman mythology. Interestingly, Poseidon appeared as a boss in Golden Sun: The Lost Age, whereas his Roman counterpart (Neptune) appeared as a summon in both games and could even be used against Poseidon.