It appears when Knight Anne directly assaults the Nest of Queen D-38 on planet Void. Stag Beetle kills many of the experimental unit soldiers present with Anne, but after a heated battle she finally kills it using AB Sword Number 10. Square loaned to her by Leo. 
It's one of the very few Beasts in the series that ever lands a hit on Anne, though she was retired and out of practice at the time.
Powers and Abilities Edit
Stag Beetle is primarily armed with a spear and has a hidden blade in its left arm. Additionally each shoulder houses a high output particle cannon capable of rapid fire shots.