Hello,
Now please note that this following tip was working as of patch 2.3.2. As of yesterday we moved to 2.3.3 but it didn't seem big enough of a patch to have any effect on this exploit.
Alright,
from what me and my guild found out, doing our first attempt on gruul, that if you are a mage, you can blink through Gruul's doors while the fight is active. This was found by accident when one of our mages, in an attempt to get away from a healer, blinked towards the door, and to his dismay, went through it.
To reverse this effect, simply blink right back into gruul's room.
This can be usefull for avoiding ground slams/shatters.
Have not tested with Shadow step on rogues, or any other abilities for other classes.