We don’t want Lord DeRosso feeling left out; when you have time, drag yourself to the seventh floor of Vampire Castle (yes, we realise it’s a hike and a half) to say "hi" to the lonely archduke. Accept DeRosso’s challenge and he’ll interrupt the start to invite a guest–Victor–to his mansion and, naturally, the forthcoming battle.
Boss: DeRosso and Victor
|66||99,999 (DeRosso) 80,000 (Victor)||Light (DeRosso) Dark (Victor)|
Honestly, with the addition of Victor, this battle isn’t really that much tougher than usual. Victor himself isn’t very menacing if you have Abate Light on your characters and the Lustrous Shield (negate Light) on your healer. DeRosso is still a threat though–and one you should never take lightly–so focus on him first; it should be easier since he has lower HP than in his solo bout.
As before, have your speedy character raise Rampart after DeRosso uses Battle Thirst to block his powerful Energy Burst move; alternatively, since you’ve gotten stronger, you can survive by just Defaulting (paired with Default Guard or Absorb Physical Damage if you’re uncertain).
Definitely try to keep your party’s HP near maximum throughout the battle, as DeRosso loves to use Graviga to make 3/4 of your party’s HP go missing or Bone Crush to deal damage equal to your lost HP. For this, it’s essential your healer is kitted out with the best Agility and Speed-boosting abilities and equipment (like the Hermes Shoes found in his castle).