A few scholars have written of the Quintapoidal Fungi, but it wasn't until Baron Lee van Hook determined them to be his "carnophytes" (laymen just call them "fungi") that he became interested.
The Quintapoids are feared by civilization, as they are living siege engines, powerful enough to batter through fortifications and with toxic spores that can easily overpower legions of troops.
Fortunately, they're rare on the Sorrowfell Plains — the Wizard's Tower only had one specimen, evidently a pickled curiosity acquired at great expense from a trading partner across the ocean. Still, the creatures have been recorded on the plains, and many old soldiers recall (typically with a shudder) their use in the Cackledread War.
Quintapoidal Fungi are occasionally found in the wild, but it is more common to find sorcerers or other masterminds attempt to capture the things as use in war and defense. Unsurprisingly, tales of failure are rather common, and form a frequent punchline in jokes, limericks, and bawdy songs throughout the land ("The mad old wizard prepared his plan to finally kill the duke / But the grand ol' beast had other plans and showed him its rebuke / And when the villagers found the Tower of Hurllenghast destroyed / The townfolk shrugged and raised a glass to Ivan, the Quintapoid!").
The following creature is a fairly common Quintapoidal Fungus specimen. In combat, the creature will typically move amidst its foes and use Gasteromycotoxin to attack everyone. The creature then cycles among Bite, Slam Harder, and Mycotic Infection, typically using Slam Harder to advantageously reposition foes (and also to attack foes resistant to poison). It uses Bite and Mycotic Infection to weaken and disorient foes, trying to take out weakened foes with these attacks.
The Level 10 version of Skinrot is functionally the same as the version noted in Open Grave on page 180, with the following alteration to the Endurance check DCs:
Check: At the end of each extended rest, the target makes an Endurance check if it is at stage 1 or 2.
12 or lower: The stage of the disease increases by one.
13-17: No Change
18 or higher: The stage of the disease decreases by one.
For DMs without access to Open Grave, any sort of rotting or wasting disease with the appropriate Endurance DCs will do.