This aura will show you a huge warning message along with the Onyxia Scale Cloak Icon when you Target either: Firemaw, Ebonroc, Flamegor or entering Nefarian's Lair.
Credits to Ora that I got the idea about this aura. Ora's original aura found here: https://wago.io/OnyxiaCloak
Ora's aura does automatically equip the cloak instead of showing the warning message.