The new Immortal tracks per-boss and doesn't require a single lockout, so will be substantially easier, although guilds attempting to be the first to get it done will undoubtedly treat it the same way they did the existing achievement, barrelling through in a single clear. An interesting question is whether you can wipe and go again, as long as nobody dies during the actual kill; we shall soon find out if that's the case, and if so, it becomes even more trivial (chain-wipe until you get a perfect kill). As several commenters pointed out, this isn't true. Shame!
This should put paid to a lot of the complaints about the new Immortal, as guilds will be able to treat it more or less the same way as any other achievement. Importantly, it will no longer cause the divisiveness it's managed in its current form. The fundamental flaws with the achievement, however, are still there: the simple fact is that killing a boss without anyone dying can and has been nothing to do with the skill or gear level of the players, but is subject to uncontrollable factors, mainly RNG and lag.
As a raider on EU-Silvermoon, I'm extremely familiar with trying to raid successfully and efficiently through lag, and sometimes it just isn't possible to execute a flawless kill if the server isn't co-operating. This caused endless frustration with our own Immortal attempts, which would go fine - if a little laggy - until Thaddius, and then the server would decide its hamsters needed feeding, and entirely seize up, leading to disconnects, delayed polarity shifts, and movement registering too late on the server.
With the new Immortal, if the server is laggy and you 'fail' on the first boss, you can come back another night and finish the achievement off, knowing you only have to kill the first boss next time to round it out. There will still be some divisiveness over who will be the first 25 Immortal Twos, but ideally people will gain the achievement for some bosses without even trying, making it easier to swap people around as needed. The main problem is those raiders who you know are complete liabilities, who will still clamour for the title, despite their presence more or less assuring you won't get it -- but that's a management issue best left to a future column. Failing Immortal
The best thing about the Immortal achievement is the schadenfreude that results from hearing someone else failed it more spectacularly than you. My guild managed, in one day, to fail both Immortal and Undying on Kel'Thuzad (to this day my main still hasn't been back to complete Undying due to the memories). I believe we had an offtank mind controlled on heroic, and a caster - who had respecced from his normal melee role - blow up on normal.
Evan writes in with a tale of three separate KT Immortal fails: frostbolt gibbing someone after mind control (fairly common), an offtank getting frost blasted with four adds (ouch), and a paladin getting MCd and casting Hand of Sacrifice on the boss (now that's painful). I've also heard of some MC-based RNG combos, including a healer getting hit with chain lightning from a MCd player, detonate from a nearby caster moving the wrong way, and frost blast all at once. Not pleasant.
Some other Immortal failures that seem pretty common include dps warriors getting too happy on Patchwerk and taking a hateful (well, you'll get plenty of rage... temporarily!); people with low graphics settings dying to Grobbulus' cloud; dps warriors (I'm spotting a theme) whirlwinding newly-spawned slimes on Grobbulus and going splat; caster tanks on 4HM not actually getting aggro from the back horsemen, and causing raid-wide damage; and of course Thaddius. The most impressive Thaddius failure I saw was when someone managed to die before the adds were even killed, though the story of a rogue crossing charges because he was too busy trying to teabag someone who hadn't actually died comes a close second. Not failing Immortal
Learning from failure is a good start on the path to successfully completing the Immortal achievement. Kyth at StratFu has written a great, detailed guide
to succeeding at Immortal, and it's definitely worth a read if you want a step-by-step walkthrough.
Some things that worked for us included having great motivation (one of our officers said he would change to a female night elf if we succeeded that week - and we did), keeping a fixed 'Immortal' team that included our best players (something that caused divisiveness and complaints from those left out), and rescheduling raids if there was lag (we finally completed it at 0200 or something ridiculous).
We were aware of our weaknesses, which were mostly based around server lag. Some guides advocate starting the clear with Razuvious
, as you can reset the instance if you wipe, and try the achievement again -- we never had any trouble wiping on Razuvious, but the Construct Quarter was our Achilles heel due to Thaddius, so we started there. People singlehandedly responsible for a previous Immortal wipe were generally rotated out of the group for future runs - we repeated the achievement with everyone who had missed out later on. We took three tanks and six healers, with a feral druid additionally tanking on Gothik, 4HM and Kel'Thuzad.
Control is the key to Immortal, ensuring you know where you're likely to fail and do everything you can to avoid it. For example, if you have a particularly laggy server and people are prone to disconnecting on Thaddius, establish secondary positioning and move the boss and raid there if people disconnect. Keep Hand of Sacrifice on cooldown during KT, use a third offtank who builds aggro on all four adds in case one of the OTs gets mind controlled (it sounds overkill, but as we wiped to that exact situation, the extra layer of security worked for us). Hold DPS on KT at around 50% until he MCs, to minimise chances of MC during the add phase. Learn your failure spots and do as much as you can to negate them. In Ulduar
Immortal in Ulduar should be less of a headache but many of the same lessons apply. Motivation not to die, knowing weak spots, controlling the encounters as much as possible, and dealing with lag will all be very important. If you die, or spot a death you could have stopped, ask yourself what you could have done differently. Constantly improve your own play and your guild's will follow.