I'm not well versed on the subject of boss coding, but I have an incident to report which yields some evidence.

On one occasion when my guild was running BWL, I was getting that bug where mobs appear as "unknown". The problem occured in the suppression room and when we started fighting the Broodlord Lashlayer, I saw him as "unknown level 62."

Has anyone else seen the true levels of other bosses? It would be interesting to compile a list.

They're 63 almost across the board.

Are there any exceptions to the rule?

You can see some boss levels as ghost entries in thott from the days when it wasn't completely masked, but none especially spring to mind. All the important ones are 63 anyway.

Define important? I consider Bloodlord Lashlayer to be important but he's 62, not 63. For that mater, the boss of Uldaman couldn't be much more than 50 elite (although I don't consider him important).

AQ and Naxx basically.

Crushing blows are done by mobs 3 levels above you. Since all the raid bosses deal crushing blows, you can safely assume that they're all 63.

Er, Crushing blows happen on you from mobs equal level and above.

I remember Luci wasn't marked for a while and was only level 61 (maybe 62), but I was shocked to see he had become Bossmarked when I revisited MC after a while.

(source: http://evilempireguild.org/guides/ their information is apparently from a official "blue" post, check the site for further info)

Here's a fun mystery:

Has anyone noticed that Patchwerk cannot land crushing blows with his melee attacks?

Yet he resists spells like a level 63....

Negative Ghost Rider. You can still find the original Blue posting on this over on the Euro boards. Devs responded to the CMs about how crushing blows worked, and stated that mobs 3 levels above you will deal crushing blows. ie, a lvl 1 noob wanders into STV - he gets dealt crushing blows by every single mob in the zone.

It would be absolutely insane if equal lvl mobs dealt crushing blows to you - how the hell would anyone lvl up?

He can be glanced though, correct?

Maybe they just disallowed him to crushing blow for whatever reason.

"OMG Amnennar the Coldbringer is level 500!"

Right, it seems that he's a level 63 mob who has 310 instead of 315 weapon skill, to put it in those terms. It's interesting because I know no other mob for whom this is the case.

It's clear why it was done. Patchwerk hits for ~2k and attacks every 0.8 seconds. A decent tank will never be crit by him and without crushings, it becomes a very steady (albeit high) stream of DPS to heal. If he could crush, the potential for horrible damage spikes would require far more full-time healers on the MT and probably make the encounter impossible without stacking healers.

Hm interesting, the only thing I could think of is that his "weapon skill" isnt equal to that of a "normal" level 63 mob. If I understand correctly, it's not the level of the mob that decides if something can deal a crushing blow but the weapon skill of the mob.

So by lowering his weapon skill to (for example) a level 62 mobs, he cannot deal crushing blows. I'm just guessing here though, so please correct me if I'm wrong.

EDIT: what Praetorian said.