The open area offered little cover besides some fallen trees that could shield him from their shadow-based attacks. Their ability to create darkness worried him most—if he got trapped in it, escape would be nearly impossible.
The clearing's size also meant that if any creature survived his initial attack, they could surround him. And with their enhanced strength, even a glancing blow could prove fatal.
The lack of trees also meant he had no high ground advantage, forcing him to rely solely on his ranged attacks. If his mana reserves depleted before eliminating all threats, he would be left exposed in the middle of the clearing with nowhere to retreat.
Sure, Erik could fly, but not knowing exactly what those guys could do with their brain crystal powers was still problematic.
Then he made enough wind blades to attack.