James McMurray said:
I guess I'm unfamiliar with 2e (played it a little long ago), so I'm amazed that you managed to destroy the Vestige. I certainly wouldn't allow Limited Wish to remove its defenses, although Wish might work (for a round or two at most).
And of course, when I converted it to 3E I used the Abomination info from the ELH. I gave it regeneration requiring a weapon forged in a dream to get past.
I don't remember the exact sequence but it involved Wishes to lower the defenses for a round whereupon the spellcasters piled the damage spells on at longest possible range. We then repeated the process for 3 or so rounds using limited wishes as nevessary to simulate other damage spells like Cones of Cold or Chain Lightning. I think it took 3-4 Wishes a Limited Wish or Two, several Delayed-Blast fireballs, Flamestrikes, Meteorswarms and lower level damage spells over about 3-4 rounds before it died. We never did get its resistances completely down, we just reduced them enough that massive amounts of damage could get though and eventually kill it.
In all fairness, our 2e party consisted of a 15/16 Mystic of Nog(from Al-Qadim)/Priest, a 11/13/15 (Rogue/Priest/Sha'ir(from Al-Qadim)), a 21st level fire-genasi fighter with a Girdle of Fire Giant Strenth and a +5 sword, a 9/12 paladin/priest with a semi-artifact level Holy Avenger, an 19th lvl Wu-Jen (using the kit from the Complete Wizard's Handbook), and a 20th lvl Necromancer (an NPC ally who we'd picked up in an earlier adventure), plus an efreet, a marid and an Al-Qadim slayer genie with Max HP and a +5 Sword of Mortal Slaying. We had been playing these characters for 5 years or so of real-time and we had accumulated a LOT of stuff and knew how to use it.
My rogue/priest/sha-ir alone carried a Wish spell stored in a tattoo on his chest, a Wish spell stored in his staff, and another stored in memory. I could also call on a Wish from the Efreet once per year and an Alter Reality (1st edition spell similar to a Wish) from the Marid. The NPC 20th level necromancer also carried 3-4 Wish spells on scrolls and one or two in memory.
Note, despite our firepower, the Vestige surprised us and routed us the first time we fought it and forced us to Teleport without Error back to Al-Qadim. The second time we loaded ourselves for bear and came looking for it and provoked a fight on our terms. As I recall, we also used divination spells and Wishes before the fight to try and figure out what it was and what might work against it. (This didn't work very well so we settled on using the Wish spells to drop whatever resistances or immunities it had and then just pouring the damage on.) Even then, it didn't go down quietly. It's just that at that point we knew that it was there and we had a pretty good idea how to kill it.
That all said, despite our levels, the adventure was tough. We had deaths aplenty (I will avoid specifics so as not to tip off your players.) We lost a PC to the Winter Wight under the Puzzle Box. We lost another to another Winter Wight somewhere else in the City. We lost a couple when we accidentally cast Delayed Blast Fireballs into an ice corridor filled with Moilean Zombies. One PC was killed by the Executioner, one PC was killed when we shattered the mirror of life-trapping (we forgot that you needed to dispel it), one was maimed by playing the game of chance, and another was killed by the dragon. Finally, all but one of us died again in the final fight when we forgot what we were supposed to do to end the Devourerer's menace forever. The last guy remembered it in time for us to pull victory out.
As I said before, Return to the Tomb of Horrors is one of my favorite adventures of all time. I love the way you are running it and I check weekly for new installments to the saga.
Tzarevitch