What I use:
Royal Jelly/Jelly King Set up
Leviathan Blade
Shivermist
Normal armor, piercing trinkets, grey owlite shield

Lord Vanaduke Set up
Leviathan Blade (unused mostly)
Shivermist
Gigawatt Pulsar
Divine Veil, Vog Coat, Grey Owlite Shield

What I'd like:
Royal Jelly/Jelly King Set up
Super Blast Bomb CTR Max (I hear 3 star weapons do more damage in tier 2 than 4 or 5*, but maybe I hear wrong)
Shivermist CTR Max (the status and extra range are more important)
Biohazard (quickly charge and poison it then continue bombing), Venom veiler CTR Max otherwise since it will do about the same, maybe better)
Virulisk Set (if armor scaling is the same as weapons)
Aegis/Omega Shell/Royal Jelly/Ironmight/Volcanic Plate shield, not sure if one of them pushes enemies farther
Dmg Trinket+HP Trinket? (CTR Trinket instead to make it easier to achieve CTR Max)

Lord Vanaduke Set up
* Shivermist CTR Max for all the stratum (this will keep monsters from surrounding you, however your party may still screw you up).
* Polaris VHigh Undead for all the levels prior to boss (it pushes enemies away from you when such party won't play nice when you freeze, and has bonus damage but you can use something else like Nitronome or Supernova or Divine Avenger).
* Blitz Needle for boss and Trojans (or argent peacemaker, I'd go needle because during the boss battle you will be expecting to be freezing the boss, so you don't need the AP high mobility which is used for a battle without a status bomber, the only time you won't be freezing is when another player is, and in that case its safe enough to use blitz needle which has better dps which will be useful to take down trojans, Barb THorn Blade isn't a gun but can fill thr role too if you prefer swords or have vog set for example)
* Leviathan for boss and Trojans (the mask phase goes down quicker to normal, since I selected Polaris you are lacking normal, if you dont want to trust your party you can use Supernova or Divine Avenger instead which are ranged and will keep you away form harm and since you can keep your distance leave you the role of extinguishing the mask)
* Normal/Elemental/Fire armor set (vog works, since you will be using guns during the boss fight Nameless Set with Max Fire would be best probably if you can get the fire resistance on it)
* Crest of Almire max fire?
* Gun Damage Trinkets to speed boss fight.