Vespa, the Spirit of Power (orange) is the boss of the Wyrm's Nest and can also be fought in the Eternal Battle.
Vespa is one of three spirits, the other two are Liora (blue) who helps your character, and Acantha (green) who is the boss of the Lightless Grove.
Vespa is a quick-moving boss who has a fire damage component in every single one of her abilities. When fought as a ranged character, she will mostly chase you around, making it almost impossible to fight her even when using skills, charms, or potions that improve your movement or attack speed relative to her own.
Vespa's main attacks are to shoot three fireballs in a cone pattern, or to shoot a small, slowly-moving flame that chases you around and then detonates on contact causing damage and knock-back. Vespa is also able to use a spell similar to your damnation spirit spell; she has a knock-back effect with this spell.
The best way to defeat Vespa on the first run may be to prioritize strong defensive gear over offensive items because her attacks cause extremely high damage and are almost unavoidable.