Suffocation Aura?

So I have an idea of what I'd like to do, but don't know how to accomplish it - or if doing so is even possible.

Basically the mob would be generating a cloud of smog around them; within this aura it would makes the player think they are underwater/losing air

- If Possible : Ability to damage the player's air supply with skills.


If anyone has any suggestions towards achieving this goal, I'd greatly appreciate it!!!