Kill Friendly Players Below 100, Massacre In The Auction House (Patreon)

An interesting exploit I discovered while finding workarounds for the "Proving Grounds" nerf.

Steps 

1. Port to Garrison using your Garrison hearthstone.

2. Talk to Seer Kazal. 

3. Chose the "Bastion Of Shadows" option. 

4. Enter the raid instance and immediately teleport out of the dungeon.

5. Go somewhere you want to kill people eg Auction House.

6. Port back into Bastion Of Shadows. 

7. Aggro the trash in front of Shadow-Lord Iskar.

8. Wait till the "Fel Raven" casts "Phantasmal Nova" on you.

9. Get out of combat and leave the raid instance.

10. Return to wherever you came from and wait for the Phantasmal Nova to expire.

11. Watch players die.

The Nova will kill any player below 100. It does not affect NPC's.

For most classes I have not found a way to leave combat other than clicking on "leave instance group", which works but means you will have to return to the garrison and Seer Kazal to set the process up again. 

Hunters can use feign death instead and then use "teleport out of dungeon".  

It is also very likely hunters and warlocks can get the "Phantasmal Nova" debuff put on their pets, then dismiss them, and have fun with summoning them and unleashing the nova later.

Since my hunter and warlock mains are both currently on banned accounts I have not been able to verify this, but I did notice the debuff going on my minion Xuen when playing a monk. Historically using debuffs on pets and dismissing/summoning them has been a standard trick used by hunters in the exploit community.

Note that this is very unlikely to be the only LFR debuff that can be exploited in this way. There may well be others which do damage to npc's or do more damage (especially in current content).