Here he is, straight from the Abyss itself.  The Devil Armor battle can be just plain brutal.  I recommend casting spells like Illusion Sun and Shadow Servant to be able to avoid attacks [Illusion Sun] and pile on the damage [Shadow Servant].  He'll summon Zelnams in every round which will make this battle much more difficult.  You'll need to use long range attacks like Backstab, Great Wheel, Megahawk, and any high level bow wazas to do any amount of decent damage.  If you don't have any long range attacks or multi-hit wazas, this battle can drag out for quite a while.  Once you have defeated the armor, you'll gain the Devil King Armor.

You're automatically teleported back to Xuan City where you're thanked by both Yan Fan and Bai Meiling.  Now you can return to the west!  But first return to the Mung Village and talk to one of the men there.  He'll mention he kept going west and saw a city of elephants.  Now Rashkuta is revealed on the map.  You can go there and explore if you wish.

This monstrosity is the Crystal Dragon.  It's big and thinks you look delicious.  Not only this, but they guard the treasure chests in the Crystal Ruins.  They're not quite as hard as they may appear, and now I don't recommend Tri-Anchor otherwise Electricity will tear you apart.  Its regular attack hits twice and may paralyze you.  Use the Tiger's Cave formation, and you'll take very little damage from the dragons.  You'll probably want to use higher level waza like Shot Wave, Split Image, and others to do significant damage to the beast.  Unlike the Dragon Rulers, these don't have inordinate amounts of HP and regenerative abilities.

Earth Abyss Gate- Devil King Palace, Pidona
Water Abyss Gate- Under the Sea, West of Vanguard
Fire Abyss Gate- South in the Jungle, South of Ake
Wind Abyss Gate- Mount Taftan, South of Loanne

Hah- I don't really consider it too much of a Boss battle, but the wonderful Boss Music is playing so...  Just use a nice hit-all waze.  Any of them will do nicely, especially Great Wheel.  I had Mikhail use that and it killed all of them in 1 hit.  The Forne Soldiers, being Soldiers of Forneus, the Water Abyss Gate Guardian, are naturally immune to Water-based attacks and will also use them.  Although you were sleeping at an inn, your WP and JP has not been recovered, not like it overly matters in this battle.  If worst comes to worst, just use regular attacks.  They only have around 1100 HP each.

Hah... The only reason I consider this a sub-boss fight is that the monsters have alot more HP than usual.  They are, however, exceedingly easy.  I recommend using regular attacks because, if you're like me, you fought all the enemies through the cave and are low on WP from mastering techs.  Besides, why waste T Potions when you'll end up fighting these guys?  If you want, throw in a hit-all waza like Holo Sword or Great Wheel for good measure.  You shouldn't have a problem with his battle.  If you do, you're definately not ready for the battles to come.

Now walk up and examine the Dolphin Statue to obtain it.  Return to Vanguard and place it in the very front of the Control Room.  Vanguard is still unable to move so it looks like you'll need to get some Water Mages from Moses to help you, but there is one problem: Moses is currently divided in a feud between Undine, the head Water Mage, and Volcano, the head Fire Mage.

He's a bit over-confident calling him self the Master of Death, but he can summon tons of undead.  That's his main strategy really.  You'll need to keep using hit-all waza such as Great Wheel, Snake Sword (if you learned it from the Kris Naga), and Holo Sword work great, even though Holo Sword will only hit 3 of the enemies.  If you're able to hit him yourself, Brook Rush has done in excess of 2000 damage so I recommend using it.  Other good waza to use are Tomahawk or any other of the Tomahawk-based waza or strong Bow waza.  As long as you keep depleting his summoned undead, this battle will be very easy.  Also, as long as you leave some of the monsters alive, he doesn't seem to summon more undead.  This will work vert well if the ones he has summoned are on the back row.  The battle ends when the Death Master dies, regardless whether or not there are monsters left.  You'll obtain the Devil King Shield after winning the battle.

I must say, this battle isn't exactly the difficulty that you might expect from some master mages...  Each of them have around 8000 HP or so, but it'll drop oh-so-quickly.  Use attacks such as Brook Rush, Southern Cross, Dynamic Hit, Great Wheel, or Split Body to deal out the damage in no time.  Using attacks like these, this battle should only last for 2 rounds.  Both of them have their seperate elements at their disposal.  Like I said, this battle is easy ;).

After beating them, neither will end up dying which they would have if you had killed one of them instead.  They realize how much trouble they've caused and change their ways... aww.  Now you can go back to Undine's and gather the Water Mages for Vanguard.  There is also a Flame Beast armor and a Guard Ring in Volcano's mansion.

This is very powerful if you are not prepared, but you may run.  It will recover 999 HP per round and use some devestating attacks on you.  You'll need to use attacks such as Split Body, Southern Cross, Dynamic Hit, and Headwind to survive.  You can Run Away from this battle which will greatly assist in learning waza from this beast.  A good way to attempt to counter the Dragon's regenerative capabilities is to use another element such as Fire to alter the "air."  Just continue to use your best waza, and the dragon will eventually fall.

Now leave the room and take the path to the left.  Walk north through the next room and then head to the left.  Take the northern path, and you'll enter a large room full of enemies.  In the northern side of the room, there are 5 chest that contain (from left to right) 1000 G, Fishscales, Sea Tortoise, Fishscales, and 1000 G.  Now return to the previous and head down and through the entrance on the left.  Go north through 3 rooms and you'll enter a curved hallway.  Walk up then turn right and go back down.

As much as it may appear to be hard, it really isn't.  Forneus does recover 999 HP per round and gets two attacks.  His physical attack will hit you twice for not too much damage.  The trick is to have either a high magic defense or armor that will make you immune to water so his constant use of Squall doesn't do too much damage.  The best way to counter his regenerative powers is Split Body.  With around 30 skill in Swords, you should easily do around 2200 damage with that waza alone.  Use other power wazas like Southern Cross, Dynamic Hit, Reverse Wind, Triple Supremecy (or Spiral Wind if you don't have that).  This battle will be even easier if you have a designated healer.  If you've fought nearly all the monsters since when you started the quest to get the Dolphin Statue, Forneus should prove to be no problem.  (I started the quest with 400 HP and had around 750 when I fought Forneus).  By going through these long quests, you have no problem completing any other of the side quests.

After killing Forneus, you will be back in the Control Room in Vanguard.  Take the city back to the main land, and you're ready to begin your next quest.  Also, make sure to return to Lance and talk to Anna.  She will give you the ultimate Water magic that was released with the destruction of the Gate.