Again, I'm going for maximum murder here. Malarys casts Greater Dispel Magic at 18th level thanks to his Inquisition Domain. Between that and Alter Fortunes from Malarys and Vee, the Bey should be stripped of most, if not all of his protective spells. Then there is the Destruction spell, which is a nice Save-or-Die effect, again with one or more Alter Fortune spells backing it up. If Malarys' doesn't succeed, Dany's will be right behind it, also backed up by an Alter Fortune. And if the asshole survives both Destruction spells (though he will have still taken 20d6 damage as a result), he gets hit in the face with 39d6 damage from Lya's Lightning Lance spell. Thanks to the Owl's Insight spells Lya cast on them, both Malarys and Dany's Destruction spells have a Fortitude save DC of 28. Resisting that four or five times in a row would be a neat trick.
I loaded out Clerics up with Cold-based spells, especially Rina, but those are for emergencies. We don't want to use Cold magic right now, not if we're going to try to sell the Ymeri angle. That's also why I don't have Viserys using Shadow of the Doom. It's a Fire spell, but also a very distinctive one which we've used several times on the Plane of Fire in recent times. Better to err on the side of caution, IMO, and not risk its use being linked back to us.
I'm including a part two to the plan just in case part one goes super smoothly.
Thoughts or suggestions? What else can we do to implicate Ymeri without going over the top?
[X] Plan "Sinanju ain't got shit on us!" Part One
-[X] Viserys casts Nerveskitter on Malarys, then uses a Searing Agonizing Firebrand spell, targeting the Fire Giants. He also hits the Bey with a Firebrand burst, if possible.
-[X] Malarys cancels his Sign spell in order to set his Initiative to 21 (26 with Viserys' Nerveskitter). He then uses a Quickened Targeted Greater Dispel Magic on the Bey to insure the Bey is stripped of protective spells and magical effects. If successful, he targets the Bey with a Destruction spell (DC 28). If the Dispel is unsuccessful, he uses another Targeted Greater Dispel Magic against him rather than Destruction.
-[X] Rina cancels her Sign spell in order to set her Initiative to 22. She uses her Rejection spell, attempting to blast the Fire Giants down the hallway before they can attack us. She uses Alter Fortune to insure the success of her spell.
-[X] Dany cancels her Sign spell in order to set her Initiative to 24. If the Bey survives Malarys' Destruction spell, she targets him with own Destruction spell (DC 28). She uses Alter Fortune, if necessary, to insure the Bey's death. If Malarys destroyed the Bey, she instead uses her Radiant Assault spell on the Fire Giants.
-[X] Lya cancels her Heightened Awareness spell in order to gain a +4 bonus to her Initiative check. If the Bey still lives after being struck by both Malarys and Dany's Destruction spells, she uses Spell Enhancer then targets him with all three bolts from an augmented Lightning Lance spell. If he has been destroyed and any Fire Giants still live, she instead hits them with her augmented Lightning Lance spell, selecting targets as she sees fits. She uses Alter Fortune to assist with Malarys' Greater Dispel Magic or Destruction spells, if necessary, rather than using Spell Enhancer.
-[X] Vee activates her Earring to gain True Seeing, then readies an action to cast Greater Dispel Magic to Counterspell anything the Bey attempts to cast, should he prove able. If the Bey is destroyed before she needs to act, she instead casts Summon Nature's Ally VII (using a 6th level spell slot) in order to Summon five Large Fire Elementals for the next part of the plan. She uses Alter Fortune to assist with Malarys' Greater Dispel Magic or Destruction spells, if necessary.
-[X] Garin activates his Earring to gain True Seeing, then prepares to use Shadow Jump in conjunction with Shadow Pounce to intercept the Bey's invisible guardian, should it be present.
-[X] Richard activates his Earring to gain True Seeing, then moves to intercept any Fire Giants which are able to withstand our initial assault well enough to be able to attack. If a single Giant remains, he attacks using Ruby Nightmare Blade. If two or more remain, he instead uses Mithral Tornado to make an attack against all of them.
[X] Plan "Sinanju ain't got shit on us!" Part Two
-[X] If the first part of the plan goes smoothly, immediately move on to the next phase;
--[X] Garin carefully plants Grey Worm's holy symbol of Ymeri so that it appears to have been lost in a struggle. The Ymeri-marked note written by Grey Worm which we used to fool the Fire Giant guards will also be left nearby, partially charred but still legible.
--[X] Vee Summons another five Large Fire Elementals (Summon Nature's Ally VII with a 6th level spell slot), then a Huge Fire Elemental (SNA VI with a 5th level spell slot), and finally a Greater Fire Elemental (SNA VII with a 6th level spell slot).
--[X] Viserys casts Arcane Spellsurge, then uses his Robes of Mysterious Conjuration and an 8th level spell slot to Summon a Greater Searing Fire Elemental, a 7th level spell slot to summon a Huge Searing Fire Elemental, and two 6th level spell slots to summon three Large Searing Fire Elementals.
---[X] As Vee and Viserys' Elementals are Summoned, they are sent out in groups down the hallway and out into the rest of the Tax Office building to wreak havoc in Ymeri's name, constantly gibbering to themselves about the greatness of Ymeri, her undying flame, her incredible beauty, etc. The Searing Fire Elementals are to focus on Efreeti and other enemies who are immune to Fire, while the mundane Fire Elementals destroy records, harry guards, and generally sow confusion. Viserys casts Searing Agonizing Mass Fire Shield on up to three groups of Fire Elementals before they are sent on their missions.
--[X] While Vee and Viserys are Summoning the Fire Elementals and giving them their orders, everyone else is quickly looting the Bey's office of anything of value, stuffing the ill-gotten gains into available Bags of Holding or into Viserys' cloak, as necessary. They are careful to Dispel any magically trapped materials.