I'm guessing you're talking about how reflective scales reflect crushing shock? Well its because the fire and lightning attacks in crushing shock count as a projectile and those get reflected back.
Start with curse and then use repeditive crushing shocks to proc your crystal shard so that the instance reflective scales drop you can insta-hit him with it.
Daedric mines, velocious curse, Mage's Wraith and Resto staff heavy attack kills almost every DK I face spamming reflective scale. If you can't kill them with that combo, streak though them and repea