-Onyxia has a "Deep Breath" ability. In vanilla WoW, players didn't know what triggered Deep Breaths(it was just random), which led to many theories and speculations. You can see some here
http://www.wowwiki.com/Why_does_Onyx...Deep_Breath%3F
What Causes Onyxia to Deep Breath More?
Raid clumping
Not enough DPS
Not enough DOTs
The group's Raid ID
The race of the raid leader
The race of the main tank
The class of the raid leader
The class of the main tank
The tone of voice of the raid leader, and whether or not he has techno music playing in the background.
Not all odd groups are on the left and/or not all even groups are on the right.
People are not DPSing very, very slowly (and by slowly, I mean f#@%ing slow).
Someone got kicked/feared into the whelps (for not being where the f#%@ they were supposed to be).
The players in the center are standing next to other people.
The real-life gender or race of the raid leader or main tank
Whether Onyxia's head is currently on display outside of Orgrimmar/Stormwind
Whether anyone in your raid has downed Drakkisath within the past 24 hours
Whether anyone in your raid has downed Highlord Bolvar Fordragon within the past 24 hours
Whether anyone in your raid has the Ashbringer (beware, dual-wielding Ashbringers will actually increase the chance of being Deep Breathed)
Whether anyone in your raid has visited this web page in the past 24 hours
The number of gnomes present in the raid
The number of Twill pieces that your raid leader has in their bag
The current time of day or day of the week
Whether the main tank is currently wearing pants or not
The amount of activity currently occurring in Barrens chat
The current DKP total of the members of your raid
The number of members of your raid that are named after Naruto or InuYasha characters
The number of Onyxia Hide Backpacks currently being worn by raid members
The number of Dragonstalker pieces being worn by raid members
The number of times that anyone from your guild has died in the Rookery
Asthma
Acid reflux
For each hardcore real-lifeless player in the raid, Onyxia casts Breath five times.
The amount of raid members that haven't gone through puberty.