After fighting the clockwork golem, the party advanced into the next chamber. This square stone room featured a small wall inlet containing 5 candle flames, as well as a 5' diameter red circle painted on the floor. Once everyone was in the room the doorway behind them vanished, leaving only a seamless wall. After a moment one of the flames in the inlet was extinguished, followed by another a short time later. The party deduced this was some sort of countdown, but there were no clues as to what was going to happen, nor what to do about it.
As the last few candleflames flicked away, the party frantically tried arranging everyone inside the confines of the red circle on the floor. But quickly changed their minds, dispatching everyone to stand outside of the circle
They should have stayed with their first instinct. As the final flame disappeared, the entirety of the room was filled with a ferocious explosion of flames. Only those things placed inside the circle were spared the fiery blast. Fortunately everyone managed to survive and move on to the next chamber through a newly revealed doorway.
The next chamber was another stone room, but this time with a pedestal bearing a conch shell. The party was weary of everyone entering the room, thinking it might again trap them all inside with some horrible trap. After trying to mitigate the possibilities they eventually conceded that the only way forward was to play along.
Again the room sealed itself once all had entered, then a soft-toned blare came from the shell and an impossible amount of water began pouring forth, quickly flooding the room. As the room filled with water the party scoured the room for any clue on how to escape, but they found nothing. Finally as the party began to float in the rising water, one party member discovered that if they placed their head under the water they could read an otherwise invisible script written there. It was a riddle which read "What always runs but never walks, often murmurs, never talks, has a bed but never sleeps, has a mouth but never eats?"
Visenya answered "A River" causing the water to rapidly drain from the room. Another doorway was revealed, showing the mad mage sitting behind a desk. The wizard's head was down and he was engrossed in the tome before him. After entering the small study the party found their feet frozen in place. Nothing they tried could caused them to budge from the spot they stood. Then the sound of a rattling chain betrayed the fact that a set of metal spikes was lowering from the ceiling onto the characters location.
The wizard ignored all their pleas, right up until the party produced a magical scroll from their equipment and began to read it aloud. Upon hearing the incantation, the mage's curiosity caused him to lift his gaze. After listening for a moment he said "Remove Curse? Really? Do you even know what that scroll is for? Hahaha, I'm afraid that's not going to be much help to you, foul assassins." and he returned to his book.
The spikes descended closer and closer, when finally the incantation was complete. The wizard's head swayed for a moment, then he went still. With a sudden jolt the mage sprouted upright waving his hand, causing the spikes to quickly recede back up into the ceiling.
With his madness cured the age, named Mordenkainen, was able to relate his story to the party. He had come to the demiplane a year ago. He had rallied a number of people to help him assualt castle Ravenloft, but the effort was ultimately in vain. The mage dueled Strahd with powerful magics, but he was eventually bested. The last thing he remembers is going over the Tser falls.
Mordenkainen said that he would need to recover his personal staff and spellbook before he would be in any condition to battle the vampire lord again, but he was able to offer some help with the party's upcoming confrontation with the hags at Old Bonegrinder. He provided the party with 4 large wooden stakes engraved with mystical runes. He said the stakes could nullify the hags' ability to shift into the Ethereal plane and escaping, as they had done to the party before.
There was only one catch, the stakes needed to be "charged" in order for them to work. Mordenkainen did not have the requisite materials, but he directed to party to the old wizard's tower on the shores of Lake Baratok in the western end of the valley.