Form: Requires a solid form of 7-9 archons all of whom have max or near-max vitals and good AR in cpk gear. A couple of druids who can evoke ooze and swap tanks is also helpful, as well as a monk or two with multiplied mirrors.
To gain access under the tower in Unseelie castle, you'll first need to kill the General Hesieno for a rusted key. Once the key is obtained, travel down to the southeast tower (or track nuckelavee) and unlock south to enter the CPK area. There are a few aggro mobs in the CPK area, so be careful when entering. Travel to the center room, which has a down exit into A Destroyer's room visible only via detect illusion.
Each form member will need detect illusion to enter his room. Check reagents and be in CPK gear, as dying in the room without killing him can become difficult to loot corpses.
Dispelling weapons and/or timepieces or redemptions are a must for killing a Destroyer, as he has a level 5000 fireshield which you'll need to get dispelled as quickly as possible. The amount of damage dealt from the fireshield is immense and can wipe out your form quickly if you are not careful. Set up the form carefully, with consideration that the front row players will take in the damage from the fireshield. Before the fireshield dispels, consider using a bow formation structure to limit the number of people taking in damage.
If you have any monks in the form, have them multiply 5 mirrors of oversight for form healing. Cabos may also help out during the fight, but are not required. The room is also no-mount.
A Destroyer encounter
A Destroyer deals a massive amount of damage to form members. He is aggro (but only on entry) and no-flee. Calm works and mixes make things easier. Once form members are ready, have everyone cast detect illusion. The designated tank should enter first, with the rest of the form members immediately following. It is of upmost importance that a Destroyer's fireshield get dispelled as quickly as possible. Heal the tank every round, as the fireshield + melee damage is heavy. Once the fireshield is down, continue to focus on healing the tank, but be careful to watch if the tank swaps as he can and will blind & swap tanks to other players in the front row. A Destroyer can paralyze and blind the tank, so have a druid capable of tanking ooze a Destroyer off while the previous tank recovers. A good tactic to survival is to swap tanks as needed between 2-3 druids, while having all form members focus entirely on healing the tanks, as well as themselves as needed.
A Destroyer doesn't have a ton of HP, and will not take too long to kill - but do not hold back on the healing. Even with fireshield dispelled, he still deals A LOT of melee and form damage.
He can be spelled up traditionally and if I recall correctly he can also be slowed, but don't skimp on the healing. Designate 1-2 people to spell him up, while everyone else in the form focuses entirely on healing. Have your monks use their mirrors of oversight when everyone's SP starts to run low. If you're careful and diligent, you should be able to take him down with no or few casualties.
Item 'the blackened skull of a yuan-ti' is type reagent-astral, alignment -300, made of bone, has keywords 'misshapen charred blackened skull dead yuanti hero astral'. This item weighs 0 stones and 10 pebbles, and is valued at 28,800 gp. This level 241 item has no special attributes. *Your archon-level must be greater than or equal to 81 to use this item. Yuan-tis look human from the torso up, so it is unsurprising that this skull looks like that of a human. The only indicator and differentiator is the bone-deep scar etched into the skull's forehead when its former possessor was alive, a powerful magical symbol that would have granted the yuan-ti immense powers originating in the depths of time. The symbol itself is nearly too powerful for reality to accomodate, and certainly more powerful than your eyes can withstand sight of, or your fingers to touch or even your mind to comprehend. Ergo, it is impossible for you to tell that the symbol is even there, if not for the blinding magicality of the skull, centered in that region.
Item 'a pair of runed bracers' is type jewelry, alignment 0, made of bronze, has keywords 'pair bracers runed powerful', equipped on the wrist. This item weighs 0 stones and 18 pebbles, and is valued at 31,950 gp. This level 241 item has the attributes: wont-fuse unbreakable nochange no-steal no-npc bind-on-wear Affects hp by 644. Affects saving-spell by 5. *Your hardcore-incarnations must be greater than or equal to 1 to use this item. *This item may be repaired 4 times. Runes proclaiming the greatness of Praios inscribe these bracers in a minuscule font. Although Praios is not a widely-worshipped deity, it seems as though at least one follower of some repute has fallen in line. The runes detail not just the greatness of Praios, however, but also the fierce
Item 'a purple and white block of a magic cube' is type toy, alignment -1000, made of unknown, has keywords 'block magic cube'. This item weighs 0 stones and 1 pebbles, and is valued at 28,800 gp. This level 241 item has no special attributes. This item has a default lifespan of 90 days. *This item may be repaired 5 times. This part of a magic cube looks familiar, although it's not exactly clear why. It has funny little grooves on its uncolored face, which seems like it ought to provide some clues, but alas. It seems to wiggle like a bean, as though there were a worm inside, but that seems unlikely. It's from gaining more, similar pieces, and discovering what this the adjacent pieces link to.