The Boar Snatcher is a giant spider boss found in Spartan Woods, at the entrance to the cave in the section of the Woods populated by Arachnosi. The Boar Snatcher appears only in the Anniversary Edition on Epic difficulty and above.
The boss has no special attacks aside from poison, which is not particularly strong. Poison resistance at around 20% is recommended, but even if it's a bit below zero an occasional use of a health potion should be enough.
The Boar Snatcher does not drop any loot except for a possible fragment of a Venom Sac, but there is a boss chest located inside the cave.