Arachne's Keeper

Arachne's Keeper is a  spawned in the Spider's Den. It has. It spawns naturally in the Spider Cave under the Spider's Den. The Arachne's Keeper has the ability to dash, leave a trail of webs, and inflict a poison debuff. When killed, it drops an Arachne Keeper Fragment, which can be used to summon the boss Arachne.

Strategies
The Arachne's Keeper can easily kill you if you aren't careful enough. If you want to avoid its attacks, try to attack it when it's against a wall or be on an elevated platform. (i.e. the mushrooms.) Make sure to avoid its webs as much as possible.