After beating the game and initiating a "clear save," the teleporter within the castle in Kolton allows travel to the Seraphic Gate, a bonus dungeon.
The Seraphic Gate can only be accessed on Normal or Higher Difficulty, and consists of many Dungeons from the original Storyline, except that every floor (except one after the fight with Gabriel Celeste) contain monsters that are stronger and longer-lasting than previously fought monsters.
Many of the floors contain a high-powered boss resembling previously battled bosses possessing High amounts of HP and boosted up stats.
The 3 most formidable foes in the Seraphic Gate are Gabriel Celeste, (found in the Vesplume tower section), Leonid (found in the Lunar Sanctuary) and finally, the Ethereal Queen fought immediately after defeating Leonid.
Their appearances are noted as both Gabriel Celeste and the Ethereal Queen both resemble Capells lost friends, Leif and Faina respectively (though this resemblance is not yet explained).
Never thought you would see this next guy again, would you? That's right, Sigmund makes an apperance. He is completely optional to fight, but there is a great reward if you do. He'll rejoin your party! Be ready for a tough one though. He has a lot of health and will murder you with Alfheim and Grinn Valesti. Avoid as best you can and counter with the same. As for prep, use any HP/MP Reign you have. Sacrificial Dolls work well for one time. Enchant with high level attack/defense and HP Reign. You'll have to do this solo so be at least level 80 or above. You wont have any time for items so have the best equipment money can buy. This will get you an achievement if you suceed so fight hard and move fast.