C307 Soldiers on the Wall

"Activate rank 2 blue crystal: Temporary base. Use the location of the Stone Winged Mantis to establish a temporary base!"

A Level 2 Blue Crystal would use up two operation points in one go. However, it would save them a lot of travelling time, so using the highly mobile Stone Winged Mantis to cut into the enemy's stronghold, build a temporary stronghold beside it