This one can be easily adjusted to fit into the caverns below the city of Ptolus.
Change out the wagons and large amount of goods in the caravan for some smaller pack animals and lighter, more limited, but interesting loads. Instead of Flinds or Gnolls consider just about any other deep living humanoid monsters.
Definitely keep everything about the Myconids in place, even the potential TPK inducing comas characters can end up in. This is Ptolus, rescue is a reasonable thing to have happen, and owing a favor leads to more adventure hooks.
In short, the PCs are with a small caravan crossing through part of the caverns when they come under attack. Tracking the attackers to their lair puts the party into contact with the Myconid colony that have a problem with the same humanoids the party is after.
The party is also after a specific red fungus one member of the caravan has offered to pay them for that he knows is near the humanoid lair.
Encountering the Myconids in their lair and exploring the Dark Forest (a vast mushroom and mold infested cavern) will expose the characters to possible mold infections of various types. Getting on the good side of the Myconids will make the task of recovering the red fungus virtually trouble free and leave them with strange allies and a supply of other molds/fungus they might need later in the campaign.
If the player characters join the fungus people for the melding ritual there's a risk of them ending up in comas. In that event the adventure has them being rescued, but having none of their clothing or possessions remaining because the humanoids attacked and slew all the Myconids, then took their stuff. The party will likely owe their rescuers a big favor and they may want to gear up and come back down for some revenge.
A success that doesn't leave the party comatose will leave them with a bunch of spores they can sell for a good bit of gold to the right alchemists, herbalists, and other interested parties.
I really like the variety of things that can happen in this adventure, despite it being a brief one.