The Abyss Dungeon Walkthrough
The Abyss is an optional dungeon that's a bit of a pain in the butt to get to, has some of the hardest regular enemies, some of the best equipment in the game and the hardest boss. To reach The Abyss what you need is Rudy's Power Glove, but it's recommended that you don't come to this dungeon until you also have Jack's Guitar since that item is required to summon the boss.
Once you have Rudy's Power Glove you need to go to an Elw Pyramid, any one of them works.... And like a raging pre teen start punching the floor with the Power Glove to get the screen to shake. When the screen starts shaking step onto the teleporter and there's a small chance that you'll get stuck in the satellite rather than be beamed to another Elw Pyramid.
This could take a few tries, the very first time I tried to enter The Abyss it took me 12 tries and I was seriously under the impression that I was being trolled about how to get into this dungeon. You don't have to pound the floor any more than a single time with the Power Glove. Just pound it once then quickly jump on the teleporter before the screen stops shaking. If you do this correctly you'll find yourself in the same room shown in the screen shot below.
Now that you're in The Abyss the real fun starts! I'm not going to guide you through this dungeon step by step as I find those kind of guides redundant, I'm going to give you the freedom to explore the dungeon your own way and only offer advice for the puzzles or confusing parts.
The first puzzle you come across within this dungeon is the lever puzzle in a room that is cloaked in darkness. As suggested in the screen shot below, start at the leftern most wall and hit the two levers closest to the wall, skip one lever and hit the next one. Confused? Click on the picture below to enlarge it for a better explanation.
After the lever puzzle there are a few more rooms to explore, some of them with chests (just above the Lever puzzle you'll find three chests with the best head gear in the game in them all in a row). If you are hung up on how to make your way further through the dungeon, look for the same plaque that's shown in the screen shot below.
When you find this plaque, you'll want to run along the wall that's just below it until you find the hidden doorway that it's talking about. The stairwell that's parallel to this plaque also runs directly into the hidden doorway too. If you can find the stairwell, just keep running south and you'll find the secret doorway.
The next spot that is likely to confuse some people is the room with the blocked off door that's also shown in the screen shot above. In order to pass through this door way you'll need to put out the candle in the center of the room, assuming that you lit it in the first place. To do this use Cecilia's Magic Vase, once the room is covered in darkness the northern most doorway will open.
In the next room you'll be confronted with the toughest Grappling puzzle you've ever had to face. Go around the left side of the room so that you can collect the treasures over there, Orb of Life and Mystic Slate while working your way towards the northern central portion of the area where you find the Power Boost item.
After you pick up the Power Boost, move to the eastern edge of this platform and you'll see a Grappling Post to the east; also shown in my screen shot below. You'll want to Grapple over here and use a Duplicator on the door that's blocking your path.
If you continue north you'll find yourself in the room that you can summon Raguragula in, shown in the screen shot on the right above. As aforementioned you'll need Jack's Guitar in order to summon this boss, without it it'll just be an empty room.
Before you engage Raguragula you need to prepare for the fight one of two ways, the first of which is to equip everyone with Goat Dolls and make sure you have enough of them for the entire fight. The second way is to use Trickster against Wojanoid enemies in The Abyss and steal Frog Badges from them. This item will nullify the damage from Raguragula's strongest attack, Volcanic Bomb.
As aforementioned, Raguragula is the strongest boss in the entire game. He has one attack called Volcanic Bomb which will hit everyone in your party for 6,000 damage or more... It's an attack that's basically designed to destroy your entire party unless you take precautions against it.
Luckily you can go the entire battle and only see Volcanic Bomb one time. The two attacks that Raguragula use constantly are Zero Armor Attack which deals about 3,000 damage to a single player on your team and Poison Breath which has a chance of inflicting Poison to your entire team but deals no damage.
What I recommend for this fight is to use your Attack Power boosting spell on Rudy and Jack while also rotating Life Guard between all of your characters assuming you're not using Goat Dolls. I'd recommend that even if you farmed the Frog Badges I mentioned earlier that you should still use Life Guard on your characters since this boss hits HARD even with his regular attacks.
Your reward for beating Raguragula is Sheriff's Star which is an off hand accessory which boosts your character in every single way. It's the best off hand accessory in the entire game.