With Blackwing Lair opening just a single hour ago, we've already seen Classic World First clears, with <Calamity> of Mograine-EU and <Progress> from Firemaw-EU defeating Nefarian and clearing the highly anticipated raid only 42 minutes after launch! Edit: Blizzard has weighed in citing both <Progress> and <Calamity> defeating Nefarian at 23:42:21 UTC. With the two kills so incredibly close together, it's hard to call either the clear winner, so congratulations to both. WarcraftLogs is still processing ranks, as these kills came in very quickly after one another, but they we can see the top ranks and their times on their Blackwing Lair Progress page, in which <Calamity> is reported ahead of <Progress>.
Progress has uploaded their clear, set to music, on Youtube.
Raid Composition for Blackwing Lair and Nefarian
Calamity used Protection Warrior tanks, 11 Healers, and up to 28 damage dealers on single tank encounters primarily composed of Warriors, Rogues, and Mages - a well min/maxed group. As a Horde guild, several Shamans were also brought for Windfury Totem, and they were min/maxed to the extreme with a plethora of consumables and world buffs, though the speedy nature of the kills made a lot of the cooldown use inconsistent and difficult to track, as not every player used their cooldowns on the same encounter in order to better spread their damage throughout the raid.
Updated to reflect Nefarian's comp, rather than the entire instance - obviously they didn't use 11 tanks!
Comparison to Molten Core Clear
Unlike Molten Core, players didn't need to both race to level, gear, and then clear the raid, making this race much shorter than the week long event to defeat Ragnaros. On the other hand, rather than clearing Ragnaros with a less than max level raid, guilds had the benefit of going into Blackwing Lair fully geared and optimized, with full world buffs and consumables, making the content much easier than anticipated. Several streamers also commented on the instance feeling easier than Molten Core overall, and some bosses flopped over in a matter of seconds with the current records for defeating Broodlord Lashlayer at 44 seconds and finishing Vaelastrasz the Corrupt within a mere 29 seconds.
Bugs on Release
However, lag was a problem, with players on many bigger servers such as Gehennes-EU struggling to even walk through Blackrock Mountain, much less actually zone into the raid, due to the sheer amount of players in the zone. Some guilds such as <GRIZZLY FROM REDDIT> (finishing rank 7 overall) also had to deal with bugs, as Razorgore adds continued to spawn after defeating the first boss, leaving them unable to progress to Vaelastrasz without resetting the instance. A similar interaction happened after the second boss, as all the adds in Broodlord Lashlayer's infamous suppression room pulled together, forcing another run out and reset. Not every guild experienced these issues, and some seemingly powered through them, due to the relatively low difficulty, simply killing all the adds and moving on.