In many forests, undergrowth is thick and tangled enough that it seems to be attempting to hinder travelers, but in some places, whether due to a malevolent spirit or the ire of nature itself, it actually is. Whenever a creature moves through an area of grasping undergrowth, the grasping undergrowth attempts a trip combat maneuver check (with a CMB of +5) against that creature. Tripped creatures fall prone in the first square of grasping undergrowth that they entered that round, and lose the rest of their movement. Creatures that move through the grasping undergrowth at half their speed (after factoring in any reduced movement speed for being in a forest) gain a +4 bonus to their CMD against trip combat maneuver checks from the grasping undergrowth, and creatures that move through the grasping undergrowth at a quarter of their speed gain a +8 bonus.
If a creature begins its turn prone in a square of grasping undergrowth, the grasping undergrowth attempts a grapple combat maneuver check against it, dealing 1d6 points of damage on a successful check and preventing the creature from moving from the spot until it breaks free of the grapple. The undergrowth can’t move or pin the grappled creature on subsequent rounds, and has a CMD of 17. For their own cryptic reasons, some patches of grasping undergrowth grant safe passage to characters of certain alignments or races.
Pathfinder Roleplaying Game Horror Adventures © 2016, Paizo Inc.; Authors: John Bennett, Clinton J. Boomer, Logan Bonner, Robert Brookes, Jason Bulmahn, Ross Byers, Jim Groves, Steven Helt, Thurston Hillman, Eric Hindley, Brandon Hodge, Mikko Kallio, Jason Nelson, Tom Phillips, Stephen Radney-MacFarland, Alistair Rigg, Alex Riggs, David N. Ross, F. Wesley Schneider, David Schwartz, Mark Seifter, and Linda Zayas-Palmer.