Kvastur
Illustrative type marker; no source image is available.
Verified against 0.221.12, 1.0.7, 25390630.
Facts
Overview
Fight this tier 3 creature with fire or a chopping weapon — it is very weak to fire and weak to chop, while poison and spirit do nothing to it. Blunt, frost, lightning, pierce, and slash all land normally, so there is no reason to switch off your usual loadout beyond that. It drops resin and wood, and a trophy worth keeping if you collect them.
Tactics
Bring fire. BogWitchKvastur takes very weak fire damage and weak chop damage, so an axe plus fire arrows or a fire-coated weapon ends the fight faster than a sword or spear. Blunt, pierce, and slash all deal normal damage — workable but slower.
Poison and spirit do nothing to it, and pickaxes are ignored entirely, so leave those at home.
It has 700 health, which is manageable at tier 3 if you keep the pressure on. The trophy and resin drops are the main reason to hunt it; the single wood is incidental.
The data does not say how it attacks or how far it reaches, so treat it like any tier 3 creature: keep your distance until you know its patterns, and do not let it close in without a plan. Fire is your friend here — lean on it.