Unholy Death Knight One-Shot Technique (Patreon)

There is an exploitable interaction between two different unholy death knight abilities.

The first is the improved death coil talent, on the sixth row of the unholy talent tree. 

The second is the pvp talent doomburst.

There is an unusually comprehensive and detailed write-up of what causes this on the official bug report forums here:

https://us.forums.blizzard.com/en/wow/t/doomburst-talent-is-a-game-breaking-bug/1637769

To summarize: if talented death coil strikes an enemy target and the enemy target dies immediately (this can be a minion/pet), then festering wounds are passed onto a nearby target in addition to any festering wounds that nearby target may already have. This will cause a large number of festering wounds to instantly one-shot that player.