Description of Achievement: Kill 200 enemies using only your dragon's main skill
Earn this in the Crimson Dragon Walkthrough.

How to earn this Achievement: Your dragon's main skill is your lock on auto targeted fire which is selected by default when you begin.

Hover the recticle over enemies until they turn red as this means you've targeted your maximum amount of enemies then press RT to fire and repeat.

The 200 you need to kill counts all enemies though the larger enemies still only count as 1.