Digimon World Dusk: Union Quest: Sortie to Loop Swamp.

After you have done the species quests, this quest will become available. Accept the quest and go to Union Room. Chief Julia will ask you to go to Loop Swamp to find the cause of illegal activity detected. Bring some AntiPoison along with you and careful with the whirlpools. You only can enter the big whirlpool, not the small ones and you cannot go back.

Once you reach there, take the Bronze Plate on your left. Then go to southwest to the next screen. Climb up and down on the left and move to southwest. Take the Speed Ring a on your top. Take the whirlpool on your left.

Follow the path to the northwest and to the whirlpool. Go to northwest. Take the DigiReviverS and go back to the previous screen. Take the whirlpool below the path. Now go straight up to pick up a GateDisk, then go into the whirlpool. Go walk the path to the next screen to southwest. Then walk into the whirlpool.

You are now in the same area with the boss, but before that, take the left path to get a MultiRecoverS. Prepare your Digimon(s), save your game and get ready to fight SkullBaluchimon.

SkullBaluchimon LV41
HP: 3500~
EXP: 1200 Dark
Bit: 1200 bits
Item: MultiRecoverS.
He is tough and takes three areas. He also has attacks that can poison you.

Once you win, SkullBaluchimon will give you D Word and leave. Return to the city to report and get 115 Tamer Points, 7185 bits and a Novice Blade.

*Dark E Area will be available after this quest.