Deep down inside, many tournament teams were relieved when the dynamic duo of Serennia/Neilyo broke apart, much like how rest of the NBA celebrated when they didn't have to deal with Shaq/Kobe anymore.  I believe SK's decision was shortsighted and they pulled a Chicago Bulls in 1999.  While the team had chemistry issues and suffered from Serennia-sama's poor coaching decisions, it was still by far the most dangerous roster in professional World of Warcraft.  We saw how well the team played when they actually ran comps rest of the world played at WWI Paris.  With a warlock that they never played with before, the team finished 3rd place in what was the most competitive WOW tournament by far.  Neilyo-kun's amazing individual athleticism, coupled with the ultimate strategist in Serennia-sama made one amazing run and defended American pride from a total collapse. 

Now the team is torn apart, Neilyo-kun is getting the Kobe at LA treatment.  He finally got "his" team, but I just can't see that roster make it deep into tournaments.  Here in season 4, we have seen a tremendous consolidation of top comps for the rogue class.  90% of them are now divided between RMP and RLD.  You build around one of these two core teams, and add secondary comps that deal with your bad match-ups.  As far as I can tell, Neilyo-kun is neglecting both comps completely, and that won't get it done come tournament time.

What about Serennia-sama?  Well he is finally going back on his warrior (about time!).  While Gosey did promise the possibility of rebuilding his team, it is going to take a while before he can come up with a strong roster.  Serennia VS Neilyo will generate a ton more traffic than Serennia + Neilyo.  While neither will acknowledge it in public consider they still play for the same franchise, I am sure should their teams meet in tournaments, there is no bigger match.  It is a shame we will never see Serennia/Neilyo playing their native classes together. But I am pleased to report that Serennia-sama actually started playing a rogue in case he has to multi-class in tournaments, and he probably won't go back to druid again.  The spec of his choice?  Deep assassination mutilate, euro-style.

You don't have to look very far to find mutilate success.  Sitting on top of the SK100 ladder is . . . a mutilate rogue with S3 daggers and full PVP gear, running the euro-style 54/0/7.  I used to believe combat mutilate being superior to assassination, but I was wrong.  You do not have the mobility of shadowstep to sit on someone and do full white damage.  The strength of mutilate comes from full poison talents that makes it extremely difficult for even druids to abolish your wound debuff, and of course, amazing team burst which is amplified by improved kidney shot.  While dual wield spec is superior to opportunity, the 41/20 spec just doesn't have enough points in assassination to maximize poison application and burst damage.

In just three weeks of playing a rogue, Serennia took a pure PVE geared rogue with <100 resilience to 2250, with the rogue/priest comp and a 75% win rate.  I didn't believe mutilate can tank warriors and shadowstep rogues with ease, but that is exactly what Serennia-sama is doing.  With master poisoner and full poison talents, he has a huge advantage vs shadowstep rogues on poison application and mobility.  With 50% resist to poisons, it is not uncommon for a shadowstep rogue to blow an entire bar's worth of energy just to get a cripple proc on him, and without wound stacks, thanks to quick recovery's +20% healing, his advantage is huge in rogue/healer mirrors.  He can burst down the rogue from 70% to 0 in a single kidney shot all by himself.

What about warriors?  Apparently with the poison talents he has, with full wound/cripple stacks, he can sit on warriors whether it is war/druid or war/shaman.  Rogue priest has a very nice CC chain via fear->blind->vanish sap.  With well coordinated burst of full energy improved kidney shot + mind blast shadow word death, warriors are dropped from 70% easily if they are caught in zerker stance with 2 hand out.  Even if it doesn't finish the job, offensive dispel on hots with a full stack of wound poisons is enough pressure to keep warrior in defensive mode until the next kidney shot.

In 3v3 and 5v5, mutilate doesn't have the same flexibility of shadowstep when it comes to teammates.  You are at your best when you get to sit on someone while your team has higher threat targets.  That is why rogue/lock/druid is the perfect comp for this.  Vs RMP you will be sitting on the rogue anyway, and mutilate does so much more damage in this role.  And in 5v5, mutilate does a very good job in Euro-comp.  The undispelable frost armor makes it difficult for even shadowstep rogues to keep up with mages for extended period of time, going on the enemy warlock or elemental shaman is probably the best bet and again, mutilate shines here as the enemy simply can't leave lock/mage open.

With the upcoming pre-WOTLK patch offering level 80 talent trees at level 70, shadow dance is probably out without relentless and lethality (or any of the poison talents) for a backstab build.  The 6-8 weeks we will spend in that particular patch, I expect most arena rogues to play mutilate after how much time they spend on shadowstep.  Inspired by Serennia-sama, I tried mutilate in a fresh euro-comp myself, and I haven't had this much fun playing my rogue in a long time.  It is too bad my 3v3 is RRD and my 2v2 is RD (maybe I can convince my druid to try mutilate in 2v2).  I will probably pick up the S4 daggers as soon as possible.  It is going to be a long season and I am seriously bored out of my mind as shadowstep.  The fact that mutilate is nowhere near as reliant on PVE gear is probably another draw.

Serennia-sama's take on mutilate rogue/priest (keep in mind this is the man who won Vengeful Gladiator in BG9 with rogue/druid):

I don't know, I've played a ShS rogue in arena (4 s3 + 4 t6 + warglaives) before and I honestly find disc priest/mutilate rogue to be more effective overall than restokin/shs rogue. Here's how it breaks down for me:

Mutilate/Priest:

Pros:
-will win every single game that has a rogue in it almost guaranteed if you play well
-much easier time vs. warrior teams than shs has it, even with a druid
-warlock/healer becomes a joke whereas it was a chore with druid/shs

Cons:
-druid/hunter is very difficult (basically have to kill pet asap then sit on hunter with mana burns)
-mage/rogue is the one tricky rogue comp (have to play defensive and outlast cd's usually)

ShS/Restokin:

Pros:
-no full-on hard counters
-can take advantage of pve gear even with nerfed cheat death
-you can actually kill druids

Cons:
-good warlock/druid will either take forever or beat you
-mut/disc priest that sits on your rogue will beat you unless druid has pve gear

I'm not gonna say I'm amazing at rogue or anything, but getting 2050 as a mutilate rogue using 69 resilience and then eventually shoulders using only ~200 speaks volumes about the strength of the comp. I personally run a 49/0/12 spec with oppurtunity and MoD, skipping out on imp expose armor and murder. I feel slice and dice is a much better finisher to use between kidney cooldowns than EA if you have PvE gear (to take advatange of high hit rating). The amount of damage you do, the number of poison procs you get, and the overall pressure you sustain is much greater doing this than using EA from my experience; and obviously a lot better than rupture since you don't have talents for it.

I'm kind of disappointed with Xom caving for ShS when he was supposed to be the "Mutilate hero" but I suppose it was done in the better interest of his RMP team, where ShS would typically be stronger overall. I feel mutilate would only work with RLD and priest/druid/rogue successfully.

In any case, it's definitely refreshing to play as this spec, especially with 4pc t6 and oppurtunity main handing a shard of azzinoth. Almost every caster or rogue dies in the 2nd kidney shot (they trinket the first) and if they don't, it's usually the 3rd. Even with only 1 set of cooldowns, with full poison talents (including master poisoner), the crit/snare resist meta gem, and surefooted enchant, a mut rogue has a 55% chance to resist crippling poison, making it extremely easy to 1v1 any rogue, hence why we've yet to lose to a priest/rogue mirror no matter what spec the rogue or priest (even shadow) are. You need a good priest that knows when to mana burn, when to LoS, when to heal, and when to burst to succeed, but if you have that, you're golden. Priests can play much more aggressively than druids and burst twice as hard, despite dreamstate druids have a damage/healing talent. A well timed mind blast, swd, and smite during an imp kidney shot is around ~5000 damage alone from the priest.

The only true weaknesses I've seen the team has fighting against is druid/hunter but you don't see many of those anymore, especially at higher ratings. But if you do, they may require a bit of dodging~

Finally, I think mutilate, despite what Xom and some others may believe, will dominate arena in wrath of the lich king. Hunger for Blood is simply one of the most amazing talents implemented in the expansion for any class, deadly brew allows for amazing poison usage and application, and infectious poisons will simply be amazing against any teams with healers, especially in conjunction with deadly brew (effectively letting you use 4 poisons at once instead of 2). Hunger for Blood is the real star though, and the possibilities of this talent are pretty incredible. I'd be suprised if it doesn't get a cooldown of some sort; but if it doesn't, mutilate will be hard to beat.