Vespa, the Spirit of Power (orange) is the boss of the Wyrm's Nest and can also be fought in the Eternal Battle.
She is one of the three spirits, the other two being Liora (blue), the one that helps the character, and Acantha (green), who is the boss in the Lightless Grove map.
Vespa is a quick moving boss with fire damage 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 even with slowing or movement boosting skills. Her main attack is shooting three fireballs in a cone pattern or shooting a small, slowly moving flame that chases you around and detonates on contact, damaging and knocking you back. She is also able to use a spell similar to damnation spirit spell, which additionally knocks you back.
The best way to defeat her on the 1st run is to prioritize strong defensive gear over offensive since her damage is extremely high and almost unavoidable.