Just curious if I'm the last one to the party on this but since when can bosses block melee attacks? A guildy was looking through our logs and found that heroic Elegon was blocking a considerable amount of attacks from our melee and tanks. Here is the link:
You'll have to remove the spaces because it won't let me put links in. (mod edit: added link)
That shows a recent log (can't remember which fight) but if you cruise through the other kills on this night and all others it definitely looks like bosses are blocking our attacks. Don't flame me if I'm the last to know this but I'm just curious if anyone else has noticed this.
Bosses (and mobs) have been able to block for at least the past 3 expansions and possibly since the beginning, and no they don't require shields to do so. They can only block from the front though, so it's only an issue for tanks most of the time. If I recall correctly they have 5% chance to block; in wrath and earlier when shield block value was a mehcanic they usually had a negligible amount so it had little impact.
I'm pretty sure that bosses couldn't block during Cataclysm.
But yeah, they can, at least since MoP. IIRC, you have a first roll for hit/miss/parry/dodge and then a second roll for hit/glancing/blocks/crit. Not 100% sure on how the crit is handled, though, I might be wrong on this one.
Yeah it's like a 5% chance to block and it isn't even a percentage based reduction. It's some miniscule amount based on the boss mobs attack power or strength or armor or something (similar to how Player block worked previously, instead of just reducing a flat 30% damage). It's almost meaningless but hey, min-maxing (and most of the time you have no reason to be in front of the boss anyway).