When you raise your battle power to 1100 your next story based mission will be to Rescue Dozer. At the end of the mission you'll find Dozer and Nex Aelio (Dragon Like Enemy)
The achievement for some reason pops at the halfway point during his fight (when the cutscene starts)
You'll still be locked into battle and need to finish him off part way.
Your AI companions can freeze Nex Aelio and open him up to a lot of damage.