Here's how it goes: You post an idea for a tricky encounter you want to throw at your party. Include party strength and setting.
Others post how they would overcome it and give feedback.
I'll start with a simple one:
>in a damp jungle
>First level party, low magic
>a faceless treant knight follows the party around (basically a walking branch in armor), swinging a greatsword at them.
>He is not bothered by any arrows or physical damage and his limbs are covered with armor so they're hard to cut off.
What would you do?
The trick here is that you included 'damp' in the description. I'll use that detail to assume that it's fairly easy to find muddy places, and then lure the rather heavy (armor!) adversary into either a mudpit, or into a muddy ground, pretty much wrecking its mobility. If there's the possibility of a muddy hill I can toss it off of, even better.
At level 1 if it's immune to physical damage, most parties won't even have the means to handle it since magic use by that point (assuming some manner of dnd/pathfinder. Always remember your system, anon!), so the encounter wasn't meant to be won so much as neutralized.
Sounds like a problem that gets solved by mobility. Making the Pretty Big Assumption that the party is faster than the treant, I'd just bounce. Preferably in a direction where I don't expect other encounters, but if I do expect other encounters, try to use the treant against them--deal with the treant for roughly a round of exposure, run in the other direction, and suddenly whatever nasties are in the jungle and aggressive have to go through that.
He mostly chops down parties, doesn't really care about trees.
The party is faster, but the jungle is hard to navigate. The party could get lost or into trouble easily, so the hunting tree will catch up.
In that case, I think it depends largely on the resources available to the party. The idea of "keks off physical damage but needs armor to resist limbs getting cut off" is M I G H T Y silly, so I'm not sure what reasoning to apply to this.
Off the top of my head, feasible options to try as solutions or pieces of solutions include...
-Apease him with some magical nature-related ability or gift while on the run
-Sunder his weapon if that's an option, his slam almost certainly does less damage
-Set fire to him somehow; be creative. Lantern oil, cantrips, random foliage, you do the math.
-Get to the other side of some obstacle he can't circumvent, if such a thing exists.
-Figure out how he senses them, and remove that capability. Get quiet? Hide? Hard to tell, with the no face. Seems like a last-resort deal.
he isn't bothered by physical damage but will be ineffective if you chop him into tiny bits. The armor is there to prevent the party from cutting off vital parts with any ease. You could try to get rid of the armor, but by then you also give it some opportunities to cut your bits off. The armor is also a flavour thing.
>Figure out how he senses them
This is a good point, I hadn't thought about that. He is supposed to be a guardian-revenge manifestation of the jungle, so maybe he could be sensitive to any contact the players have with trees and foliage. I'll think about it.
Nobody else has some contributions?