Nah, doesn't work. Tried it in 10m last week, vanished with .2sec left on the Mark cast, still got it.

Pretty sure this happened with Killing Spree as well ...
Had a tome nearby ( too nearby ) Sindy in P3 - ended up inside. Was a bit confused at first.

Definitely a bummer on Vanish though - got the "noob" callout from the raid when I "missed" my Vanish on Put.

Regarding entering the ice tombs during Sindragosa's air phases: I've seen it done repeatedly by non-rogues the last time we killed her. The two people doing it were, specifically, feral druids (one cat, one bear).

The reason I'm posting this is that, unless they have some special talent I missed, anyone can get inside the Ice Tomb to dps it without getting the blasts and without getting tombed either. Apparently, it's simply good timing: if you jump onto the person at the moment the bomb Sindragosa shoots hits them, you get in without being frozen yourself. I'll test this on our next tag.

Feral Charge maybe? That's just speculation though, I'm not sure.

Can someone confirm whether this is still true in 4.0.1? Did Festergut HM a few days ago and got KO'd by blight after CloSing malleable goo. Was not watching my buffs at the time as I was not expecting any funny business.

I was under the impression that we weren't vanish-immuning Tear Gas and Blistering but rather dropping ourselves from the available targets table. Also that this could be done anytime during the cast not just at the last second.

Playing as Subt at the moment seems to have some nice perks with regards to movement:

Marrowgar: You can Shadowstep the spikes, instead of having to walk through fire.
Deathwhisper: Naturally, Shadowstepping from boss to adds and back is handy.
Gunship: I haven't tried this, but I assume you can Shadowstep to the enemy boat via the riflemen (Horde).
Rotface (Heroic mainly): You can Shadowstep the big ooze when you get Mutated Infection (Is that the name of the debuff c/d?), after it's been dispelled (You can of course dispell it yourself).
Princes (Heroic mainly): Shadowstepping is really, really nice here, as you can totally avoid the debuff you get from moving.
Lich King: I have not tried this, but I wonder if it's possible to Shadowstep the Valkyr after she drops you, to get back onto the platform (Similar to how you can use Killing Spree on the Valkyr to get back onto the platform).

Overall, I really like the playstyle of Subt and the doors it unlocks with regards to movement.

Shadowstepping back to the Valkyr should be much easier then using Killing Spree since it has 15 yards more range allowing you to wait a little longer to hit it such that the Valkyr’s back is above the platform when you use it. Though with that range, I think you will be much more successful Shadowstepping directly back to the Lich King or to another Valkyr (if your Valkyr was not stunned/slowed properly and got ahead of the others, which is generally when your Valkyr is not going to drop below 50%). A few other encounters in terms of cutting down running around are Putricide (going between the boss and slimes during double ooze), Sindragosa (after blistering cold and perhaps getting to and from the blocks during the second phase), and Dreamwalker (general movement between adds).

My the only problem I can see is that the Valkyr flies up before flying over the platform, so you may have fallen too far before you can Shadowstep back up safely. I'll have to test this next time I'm doing LK.

Yeah, that was the problem with Killing Spree where if you did it too soon or when you were 10 yards down, the Valkyr’s back would still be over the ledge so in combination with an engineering cloak it would work sometimes (basically you have a smaller window of opportunity with Killing Spree then with Shadowstep). Like I mentioned before, I think it would be a vastly better idea to just Shadowstep to the Lich King or any lagging Valkyrs.

But if you fall below the level of the platform you will be out of LoS of LK/ Other valkyrs often. Overall, I think this can work, but it won't be a guaranteed method.

When we got our LK kill prior to the 4.0.1 patch, I just went with my shadow dance pvp spec to be able to single-handedly cheap shot all 3 valkyrs and be able to shadow step my way around. I successfully saved myself several times shadowstepping to lk or the valkyr that dropped me back over the platform. While this is a dps loss of course, dps wasn't an issue for us, it was valkyr control. I didn't feel the need to post it before since I figured it would be viewed as too big a dps sacrifice and "your guild sux" comments, but for a guild that isn't as good as you'd like and losing 1-2 ppl every valkyr spawn, making the sacrifice to get them under control was what it took for us to get our first kill - even if it meant I was doing less damage.

And ironically now that you post about it it won't work (or at least not as good) as before the patch, since KS and CS are now on the same diminishing return, i.e. with almost all other stuns.