In this corner, Onyxia, taking an afternoon nap.

And in this corner, a rag-tag band of forty challengers.  Who will win?

In typical Blizzard-style humor, Onyxia seems to like to randomly get up and stroll around the area.  She did so twice while the raid party was organizing itself, causing the party to scramble.  I understand that Kronos actually enticed her to do this the second time by sending an Eye of Kilrogg to where she was sleeping.  Onyxia saw the eye, killed it, and then took a stroll before settling back to her regular spot.  Bad warlock!  Bad bad warlock!

The party finished organizing and buffing itself.  The time for battle was at hand!

Battle erupted and Onyxia yelled out:

Onyxia: How fortuitous.  Usually, I must to leave my lair in order to feed.

Clearly a 40-person raid group was not going to frighten her away.

She broke out of the melee pack somehow, (death of the warrior tanks?) and charged the back rank of spellcasters.  Things were not looking good.

More than half the party had died and we had hardly dented Onyxia's health bar.

This wasn't just a beating.  This was a rout.