How much wood would wood woads woad if wood woads would woad wood?
Those travel-size treants are medium 8 RHD plants. Stats are 'meh' (17 strength is the highest, while 7 intelligence is the lowest), speed is moderate, natural armor is hardly impressive. No natural weapons, not even a slam.
In terms of special qualities and abilities, wood woads have vulnerability to fire, free Lightning Reflexes (weird tbh), and the usual plant immunities, in addition to some more complicated traits.
Firstly there's Warp Wood, which lets them, well, Warp Wood at-will. WW is, let's be fair, a pretty underwhelming spell. Aside from a few niche uses that a battleaxe could do too (sinking ships, opening doors), it can disable ranged weapons and impose penalties to melee weapons. I guess that a reversible sunder can be pretty useful under certain circumstances, but foes get a save to resist it and it only works on wooden items.
Secondly, there's Treewalk: an ability that allows the wood woad to enter trees. When it does so, it senses any trees within 60 foot that...
Uh, it senses any trees within 60 foot that can, uhhh... Y'know what I'm just gonna quote the rules here.
WotC, I get what you're trying to say here but at the same time why.A wood woad inside a tree senses the world around it normally and automatically knows which trees within 60 feet are living and can accept its girth.
Unfortunate phrasing aside, Treewalk is kind of bad. It requires large, reasonably dense trees to function, and most importantly doesn't allow the wood woad to take nonvegetable items along. Metal arrowheads? Leather armor? Anything with gemstones or glass? The wood woad can't use them, or it gets locked out of one of its main abilities.
Considering that the wood woad offers a fairly unimpressive chassis and doesn't have great special abilities either, I think -0 is the obvious assignment here. In the end, this is still a monster with twice as much RHD as CR, and those tend not to be great characters.