Simple enough: get through Eternian Central Command in one piece. Once you defeat the Grand Marshall and return to the World Map, you'll see the sub scenario icon pop up on the map, northwest of Eternian Central Command.
Despite this, I do not suggest pursuing this sub scenario immediately after completing Eternian Central Command. The monsters involved are quite brutal, and you'll probably want to be in the 60s or 70s before you take any of them on. This number grows if you wait until Chapters 5 and beyond, so I recommend getting it out of the way before proceeding to the Pillar of Light.
- Using the Medium Path from Eternia to Eternian Central Command, travel to Vampire Castle. If you try to accproach this place before beating Eternian High Command you'll be quietly rebuffed; now, though, you can approach properly.
- The door still won't open. Nevertheless, the mystry voice of DeRosso, who figured into the events of Eternian Central Command, will give you a hint: find six keystones. What's that mean?
- The answer is simple enough. During your journey you've no doubt noticed several stone monuments scattered about the lands. Up 'til this point they've been utterly no use to you, and didn't even warrant an inspection when approached. These are the keystones, and you have to find them all to open Vampire Castle. Let's retrace our footsteps 'round the world!
- The first keystone is on Caldislan soil. Park near Lontano Villa and you'll find the keystone on a small cape to the northeast. Approach it... and a monster will appear! Yegads! This is true of all of the keystones, which means six battles with six dragons.
- The second keystone is jammed against the mountains a short ways northwest of Ancheim. Look north of the oasis.
- The third keystone is north of the Yulyana Woods Needleworks, in the middle of the forest.
- The fourth keystone is between Grapp Keep and Starkfort on the western continent.
- The fifth keystone is northeast of Florem, on a large island. Look at the tip of the island chain that stretches northward to the semi-circular island in the northeast corner of the map.
- The sixth keystone is on the edge of a beach on the southeast corner of Eternia. Look for a small patch of yellow land marking where to stop.
Jabberwock, Wyvern, Shinryu, Salamander, Mizuchi, Ladon (in that order)
Though you're facing six different dragons on this quest, they're all more or less the same beast with slightly different elemental leanings. The dragons follow the same attack pattern: they try to hit your team with an elemental attack which will sometimes cause an additional status effect. They'll further bolster these attacks by using an Eye attack on you that makes your whole team weak to their breath attack's element. If they're not doing these two things, they'll Bite for a decent amount of damage. Jabberwock is dark, and inflicts dread; Wyvern is wind, but inflicts nothing; Shinryu is holy, and inflicts blindness; Salamander is fire, and inflicts nothing as well; Mizuchi is ice, and inflicts stop; and Ladon is earth, and inflicts paralysis.
Your tactics will be generally the same four the six dragons. Bring in one or two fighters who can target their weaknesses while one character heals and another buffs your team (healing and buffing may be one and the same). Ideally you want to use the Spiritmaster ability Greater Fairy Ward to undo the weaknesses inflicted by the dragons, as well as strengthen yourself against the dragon's attacks. Then just beat on it until it dies. It is highly, highly recommended you equip items to ward off the status effects - having to pause to use Esunaga on everyone can really put a damper on your healing efforts.
- Each time you defeat a dragon you'll earn a keystone. Once you have all six, take them to Vampire Castle. This will open the way.
- Welcome to the world of Lord DeRosso! Start by heading north through the art gallery. You'll get a bit of a history lesson from DeRosso before he vanishes again.
- Back to the first set of hallways. In the west of this area you'll find a blue chest; note its location for later. In the east is a Dragon Fang. Skim the southwestern wall to find a hidden passage, wherein you'll find a Blood Blade.
- Back to the big painting in the north. West of it you'll find a Safety Ring. Go east for stairs out of here.
- 2F. Follow the east wall to the south to find Hermes Shoes, then wander west. Against the far west wall you'll find a Black Belt.
- Enter the middle of this area. Another large picture awaits your inspection, and a Party Chat comes next. Head west to find stairs.
- 3F. Wander all the way south in the next hallway to find a Soul of Thamasa. Then double back and take a right. The passage eventually twists in to another painting. East of here are more stairs.
- 4F. Head south. You'll see a nearby chest; inside are Dwarven Gloves. Enter the middle of the area and twist to the west to find another chest, this containing Hyper Bracers.
- Painting ahead. You can guess what happens by now. Stairs to your left.
- 5F. Take a right at the stairs and head south. You'll find Magic Armlets nearby. Return to the stairs and go south; on your way east at the bottom of the room you'll find a chest in an adjoining chamber, this containing a Lamia's Tiara.
- Yet another painting beyond. Oooo, twisted history grows ever more twisted. Straits to your right!
- 6F. Head south until the corridor splits. Go right to find a Megalixir. Then follow the path west and, ultimately, to another painting. Stairs!
- 7F. Head south to find a painting. There's a robed save dude ahead, and north of him a chest containing a Lilith's Rod. Collect it, run back and save, and enter the central chamber to confront DeRosso. Doubtless you can guess what happens next.
Yiiiiikes. DeRosso is wise to warn you about his combat prowess before the fight, as he's ridiculously strong at any point in the game. True to his vampiric nature, DeRosso will suck out your life force - or, in this case, your BP, using Battle Thirst. He'll pretty much always use it on Energy Burst, which will hit everyone for ridiculous amounts of damage, or Bone Crush, which also hits everyone - and becomes more powerful the weaker your characters are. The two of these attacks one after the other will almost certainly kill your whole team. Periodically he'll also use Gravija, which is equally as devastating if followed up with by Bone Crush.
The key in this battle, more than ever, is to keep your HP high. This is important in every battle, of course, but so long as your HP is at or near maximum Bone Crush will be useless. Watch out for Battle Thirst, as it almost always precedes Energy Burst, and always go Default when Energy Burst is about to go off. If you have a swift Templar on your team you can also use Rampart to nullify the effects of Energy Burst or Bone Crush. Hit DeRosso with holy attacks to bring his HP down as quickly as you can manage. Eventually he'll fall - though it will invariably take a while. He has a lot of HP.
- Defeating DeRosso will earn you the Vampire asterisk, a powerful late game class that should serve you well. He'll also permit you to view the final painting. Make sure you do - it's quite important to the plot.