I've always found Assassination to be... strange... In PvP at least. It's rather hard to keep Slice running, and your energy generation relies on a buff that's also hard to keep track of in such a chaotic environment. It's a sluggish spec, with next to no burst, and keeping up pressure seems rather hard.
Then again, I'm a fucking moron when it comes to PvP... So what do I know..!? :P
Yeah more energy is not bad for muti you now can get starved quickly.
I don't see any trouble with keeping track of bleeds, and to refresh snd is nifty after all. I also like the idea that I don't "have" to get behind the target (although very much preferable) since better opponents, some server lag can really make it hard to stick on a target behind him out of roots, stuns etc.
Mutilate with shuriken toss is pretty crazy. Since shuriken toss lets you autoattack and proc poisons from 30 yards away, you can keep up the majority of your sustained damage even when rooted or being kited, while gaining combo points and pooling energy for burst when you do get back on your target.
I'd like to try out muti in a more serious pvp environment as well. I can actually beat warriors in duels! (ok there's only been two duels and they were no multi-ranks glads or whatever). However, my only arena achievement is 'Step into the arena'. I don't even have 'world wide winner', so I reckon I'll never get far But yeah, I think it might work if you're able to stick to one target, and let rupture going.
If you find a team, try it out