Killer Kappa Bonsai Oak

The title is in no way hyperbole. I came up with this monster on the fly when I ran Wolf-packs & Winter Snow on Sunday, using the random carnivorous plant generators in the book and wanted to remember some of it for later. Because they always come back. Almost always. Also I succeeded in really unnerving my players.

At a basic level this is just a twisty oak the size of a large bush, between the height of a halfling and a man. The oak grows in fens and marshes and generally tries to sneak up on living things, grab them, impale them, and then slowly drain their blood. It sneaks because it is very slow - a child could outrun it. It's really best adapted to grabbing small animals, especially birds, but by some maladaption it hunts many things it comes across. Certainly humans. It's quiet and stealthy but also reeks of carrion, since bits of blood and viscera seep into it over time and the branches get sticky. If someone beats its stealth, play up the smell.

like this but way smaller

Stats: Per Carnivorous Plant, with 1d4 branches and 1d6 vines. See below for other mechanics.

It will use one of its vines every turn to try to grapple and then pin (p30 WPWS, idk how universal those rules are really). The oak has a +2 to its grapple on the first turn, and every turn it's successfully maintained a grapple gives it another +1. Once they've been pinned successfully for three turns, they are impaled on a high branch and take 1d6 damage per turn to flesh. This will heal 1d6 flesh for the tree.

At the top of the main trunk of the oak is a hollow going down inside, usually for a foot or so. This is filled with acidic (and truly rancid)water and the bones of its usual prey - small animals, especially birds. Anything left inside slowly dissolves to the tree's benefit; it's basically an exterior stomach. The bones and also a caked-up white residue at the bottom may have use for an enterprising crafter or medical type. (My players also salvaged the vines for rope.)

More notably, when the hollow runs dry, the oak stops moving entirely. (Which got more suspicious stares than anything else I threw at the guys that afternoon.) Usually this is just weird, descriptive flavor to landing your final hits to its flesh - you've hacked aside the branches and shaved off the side of the bowl, and as the last water trails away it just goes utterly still. In later encounters with the oaks the players can get creative about knocking the tree over or piercing the side of the bowl instead.

But unless you completely destroy the bowl, the tree will reanimate the next time water gets into that hollow. A tipped-over killer oak left alone in the fen will get a bit of water into it during a rainstorm, and slowly right itself, and once refilled it's back in action. And it holds a grudge.

As such they're not just ambush predators but endurance pursuit predators, when the hunt calls for it. On the trail of someone they've been 'killed' by, using vibrations and scent and heat, the killer oak will leave its home fen far behind and slowly drag itself across the landscape. You can always outrun it, but it will always come back until you figure out how to stop it for good.