28th Day of Ready'reat, CY 580 - Continuing the Battle in Lolth's Temple

With seven player characters and over 20 high-level enemies on the board, this was the most complicated battle I have ever had to run as a DM. The last session was chaotic and slow as I flipped through books to look at NPCs, we lost track of initiative more than once, and it was hard to remember who had what spell effects on them. Some people were going on the wrong initiative, took too many attacks per round, or not enough attacks. I spent the intervening two weeks putting together a spreadsheet with all of the relevant information that we could step through in initiative order. I shared the spreadsheet on a screen for everyone to see, which means the players could see the effects and hit points of the enemies, but the sanity was well worth it. I also invested in purchasing digital, searchable scans of the Priest Spell Compendium and Wizard Spell Compendiums (thanks DM's Guild https://www.dmsguild.com/) so I can quickly search for spell descriptions as-needed because despite playing for decades, I have never memorized what any of the spells do.

Despite all of this, the remainder of the battle still took four hours. I couldn't begin to describe the details here, but I can summarize some highlights.

 - The hasted Glabrezu cast Reverse Gravity, which didn't affect the drow who could levitate, but everyone else "fell" 50 ft. to the ceiling, taking some considerable damage. The demon was killed shortly thereafter, ending the Reverse Gravity spell, and causing everyone to take damage again from falling back to the floor.

 - The paladin, Sir Fenius Agrivar (Fen), was the star of the show. With his Holy Avenger, combined with Gauntlets of Ogre Power, he was doing +22 damage per hit to all of the chaotic evil beings in the room (which was all of the enemies). The drow tried everything they could to take him out of the fight, but the 50% magic resistance bestowed by his sword, combined with bonuses to saves and the ability to dispel magic, he shrugged off just about everything thrown at him.

 - At one point, the High Priestess cast Lolth's version of Sticks to Snakes, which creates giant spiders. She filled the battlefield with 16 giant spiders to keep the party occupied while she cast more spells. Sebastian responded by pulling out his Pipes of the Sewer and summoning 90 giant rats, which engaged the spiders to a standstill, effectively taking them off the board.

 - Another dozen or so drow, all high-level, came down from the upper levels to join the fight. Two captains were using Death Lances, which can drain levels on a failed save. Dalron lost three levels and was rendered unconscious.

 - Fen dispelled the Blade Barrier around the High Priestess, then killed her, thus getting rid of the spiders. Shortly thereafter, one of the clerics coming down the stairs cast Silence 15 ft. Radius on Sebastian, silencing his pipes and causing the rats to disperse.

 - Sarril cast a large Wall of Stone over the stairwell, causing a massive amount of stone to crash down and get rid of all of the new drow that were coming down. This allowed Fen to finish off the last couple of drow captains, avoiding level drains as he did so, and bringing the party to victory.

But this was not the end. Standing by the tapestry, behind the illusion of Lolth, was another drow. The most beautiful drow woman anyone has ever seen. Her dress was flowing in an eerie, irregular way, which the sharp-eyed PCs could see was because the dress was made of thousands of tiny, living spiders crawling around. There was no doubt now that this was Lolth herself.

As it turns out, Lolth had been summoned by the high priestess shortly before the party infiltrated the temple. That was why the altar on the lower level was covered in fresh blood. Lolth appeared in a room at the end of the webbed corridor, which the party decided to ignore. Had they gone immediately into that room, they could have fought Lolth first, while at full power, and easily defeated her. Once defeated, all of her drow followers would have been temporarily stripped of their power, including magic-resistance, and the party would have been able to easily defeat everyone in the temple. But they, unknowingly, took the hard way, and now have to face Lolth after being severely weakened by their previous fight.
Lolth held out a platinum egg that looked exactly like the one they already possessed. She addressed

the party "I know why you are here. The egg you have is a fake, planted by me personally. This is the real one, and if you want it, you must prove your worth by defeating me." She then transformed into the spider-demon depicted in the images everyone has now seen.

As Lolth was speaking, the party was desperately quaffing healing potions. Fen decided to commune with his holy sword, asking it to grant him the power needed to defeat this goddess of evil. The sword answered, giving him the power to cast a full Heal on himself. The battle started with Lolth jumping up to the ceiling and casting Slay Living on Fen, who made his saving throw but took serious damage nonetheless. She was actually waiting for the party to get close enough together that she could dispel the effects on them, like Haste, but the party was smart enough not to clump together. Dalron headed south to collect daggers from dead drow while Sarril cast Fly on Fen and Tyril who flew up and engaged her in melee.

Lolth responded with a Mirror Image of her own to slow down the dagger attacks against her and cast a Cone of Cold, catching both Fen and Tyril. Being a high-level caster, she was able to penetrate Fen's magic resistance and he subsequently failed his save, taking a lot of damage. Her next move was to put up an anti-magic shell, enveloping herself, Fen and Tyril. With nothing to anchor themselves to the ceiling, Fen and Tyril fell to the floor, with Fen taking enough damage to reach negative hit points (though, as a paladin, he was still able to fight).

Lolth could have stayed in her anti-magic shell indefinitely. Since she requires magic weapons to take damage, and all weapons entering the shell become non-magical, she was effectively immune. But this limited her ability to do damage as well, and she wasn't going to allow them the privilege of entering her realm without fully testing them. She dropped the anti-magic shell and cast a full Heal on herself to wipe out the damage done so far (which was significant due to the extra damage from the paladin's holy sword). She then cast Feeblemind on Sarril, who, due to an amazingly lucky saving throw, was able to resist. And that is how we can describe the rest of the fight. Lolth throwing multiple offensive spells per round and each party member making their saving throws while slowly whittling down her hit points. Sarril read Bigby's Clenched Fist from a scroll and, even though it failed to penetrate her magic resistance on most rounds, it did connect a few times. Altogether, it was enough, and Lolth's avatar was soon defeated.

The truth is, Lolth could have chosen to gate in demons every round, or even teleport away, buff herself, and come back stronger, all of which would have made the fight much more difficult. But that was not the goal. This was a test. Lolth was sizing up her enemy so she can prepare to fight them in her own realm. She accomplished her goal.

Once her avatar was destroyed, the egg fell to the ground, where Shan-Ju, who had been climbing a nearby wall, leaped at the egg and caught it. The party decided they needed to act quickly before more drow showed up, but they were unsure which egg was the correct one to use. Sarril cast Identify on the original egg and got no useful information, so he placed it in the impression to try. The temple began to rumble, there was a flash of light, and then a Nalfeshnee (Type IV) demon appeared and attacked the party. The demon was able to damage several of the party members with an area of effect spell, but the party responded to bring the demon down pretty quickly.

Figuring it must have been the wrong egg, Sarril swapped the eggs and the tapestry before them came to life, opening a portal into a foggy scene beyond. Not having time to search the bodies, but figuring the high-level drow in the immediate vicinity must have good loot, the party tossed the dead bodies through the portal before jumping in themselves.

They now found themselves in a strange fog-filled tunnel. The portal behind them was now gone. Light penetrated the fog 60 ft. ahead, revealing a wall of fog 10 ft. to either side and 50 ft. above them. The floor seemed to be made of the same gray fog. This must be the Abyss.

It is evening of the 28th Day of Ready'reat, CY 580 - at least on the Prime Material Plane it was.