Tested & Working on WowScape, wowlegion/wowcrack server
This exploit depends on the fact that some servers now have mobs that are scripted, ie. they have spells.
The only problem is that they're not fully scripted. All characters mob, or whatever have a 1 s global cooldown on their skills. unfortunately, as far as this ascent update, mobs do NOT have the 1 s global cooldown. You simply must locate a mob that has an instant - cast spell and repeatedly cast it, with no CD. If you macro it, you can cast the same instant cast around 100 times per click resulting in insane amounts of dmg.
I'll give you an example,
in SSC (Serpent Shrine Cavern), 25 man instance I have solo'd you can take control of the Hate-Screamers: Thottbot World of Warcraft: Creature: Coilfang Hate-Screamer
MC them, and cast their "Arcane Blast". I macro'd it so it does it ~100 times per click, each time doing around ~4k dmg. This is 400k dmg per click. Click it a couple of times and any boss is dead. Lady Vashj died in about 3 seconds.
Other instances that have instant-cast mobs I've found are:
SSC - Coilfang Hate-Screamers (Arcane Blast)
ZA - Aman'shi Windwalkers (Frost Shock)
BT - Shadowmoon Blood-mage (Life-Siphon)
TK - Thaladred Darkener (Whirlwind.. or something like that)
Make sure you hurt the boss when your mob aggros so you get the loot!
There's an example of the hate screamer in SSC:
I Admit, its a bit more work than a simple exploit, but it does work and youi dont have to roll against 24 other players, so..
Enjoy.