The Most Gamebreaking Legendary In World PVP (Rogue only) (Patreon)

The rogue legendary "The Dreadlord's Deceit"  increases the damage of fan of knives and shuriken storm by 35% every 2 seconds, up to 1050% of normal damage. 

For a decently geared rogue this should allow them to one-shot any player in the game. As these are aoe abilities, you can take out entire raids with it.

The aoe abilities cannot be spammed, the extra damage is reset on usage, so it is a one-time only deal. 

The damage this item  is capable of producing would on the face of it appear to be an exploit, however Blizzard have a history of giving rogues stupidly overpowered weapons, for example the "Soul Capacitor" item in Warlords Of Draenor, so it is unlikely players will get banned or experience other countermeasures.

There are probably other applications for this item, particulary gold farming.