The hangman tree is not subtle. According to the flavor text, it “looms above a field strewn with bones.” Its vines are “looped into nooses.” Corpses hang from it like fruit. Its Stealth is –2—about as bad as an untrained human with a Dex of 6. If the hangman tree were the murder house in your neighborhood, it wouldn’t be the quiet ranch that smelled subtly of ammonia…it would be the gothic edifice with a clown-driven, blood-spattered ice cream truck out front and a neon sign reading “MURDER HOUSE THIS WAY.”
And that’s what’s so fantastic about it.
Other monstrous plants rely on subterfuge. Let them. The hangman is a CR 7 death tree, and all the Perception in the world won’t save the PCs if they get caught in a cloud of its hallucinatory spores. I haven’t faced one of these in game, but there’s probably a lot of fun in role-playing the poor stoned character stumbling over the bones of past adventurer fertilizer while his friends protest in horror. Let assassin vines be sneaky—the hangman tree is too busy hangin’.
A murder of talking crows is said to have the gift of prophecy…or at least a lot of good local gossip. The crows nest in a hangman tree that slowly trundles through the downs, moving slightly in the dark hours of each night.
A town in the path of an army of fey is spared when it promises to plant a tree in the center of the village green. The gifted tree turns out to be a hangman tree. Already folk are losing livestock to the tree’s vines. But if they remove it, they will have an army of spriggans, quicklings, redcaps, and fey ettins at their doorstep.
Various monsters sometimes lair in the vicinity of hangman trees. Angry or vengeful victims may rise as wights, still trailing the vine noose that killed them. Sprites find hangman trees a safe place to rest after their revels. Shocker lizards tend to drive the trees away, though—hangman trees instinctively fear their electric shocks, and the territorial reptiles scare off potential food for the tree.
—Pathfinder Bestiary 2 152