Not a Repost - I think.
For all Unholy DKs @ PvP....
Before the Arena match starts:
1. Cast 5x Death Coil on your Ghoul
2. Wait until 2-3 seconds before the game starts and use Dark Transformationl
3. Get in fight with Ghoul Monstrosity :>
4. ???
5. Profit! Why? You save Runic Power for making damage, because you don't need to feed your "normal" Ghoul with Death Coils for its transformation for the next minute.
=> In my eyes: Big dmg push.
Bug/Exploit? Yes. Because it's not working as intended. Blizzard doesn't want this to work like it does at the moment.