West Marches: Westmoor
These are trees. Well…they look like trees. They are trees. They’re evil trees. They are undetectable unless you can sense magic, as they look and taste no different from regular trees. The only difference is, these will attack if threatened. They do moderate damage, but they usually appear in numbers. The scariest part is, different trees attack different ways. Deciduous are prone to clubbing you to death, while conifers are more likely to majestically spray you with needles from afar. These are dangerous, make no mistake. On the plus side, you’ll be smelling of the freshest pines while you’re being bludgeoned to death by a future chair.
One other type of tree monster, though potentially a different species altogether, is nothing but a massive amalgamation of wriggling vines. No one has directly engaged one of these in combat but it was discovered they are incredibly susceptible to fire.