There is an engineering tinker - Mind Amplification Dish, it allows me to control an enemy with some non-100% probability. Thing is, controlled enemy is considered a pet and can be used in conjunction with Grimoire of Sacrifice to boost yourself and kill an opponent. I ask you to double-check this since I tried it only once yesterday before logging off - it may be a random bug instead of a regular one. My pet was not out when I performed this.
Maybe. But there is already a thread on Blizzard forums about that so I don't see any harm in posting this here. And this trick is quite limited - you can't use it on arena, tinker CD is 10 minutes and I'm not sure about the duels (I've tried it in world PvP).