Well I am going to look into the Empyrean Carbuncles now. My human legendary swordsman was just going about his business after slaughtering an outlaw camp, then something like "Empyrean Carbuncle uses Bladed wind!" twice and my character would slowly suffocate. Twice. One hit, and my legends ended.
So here are some arena tests on them:
Human swordsman with a steel katana and grand master skill vs carbuncle: Human dies in one hit. "Carbuncle 1 slashes the human in the lower body, tearing the fat! The human is struck down".
This itself is impressive.
Fully armored in iron human swordsman with a katana vs carbuncle:
Test one the human cut off both of the carbuncle's legs and it bled to death.
Epic carbuncles?
I then tried building a new one to fight again, to see if their blades attack is only a once and a while thing.
And the carbuncle won this time. One attack to the head that bounced off his iron helm, then one to his arm and he fell dead. Apparently I didn't armor him well enough. But now I will use a carbuncle for each test.
Now I will go straight to dragon...
And it tied with a dragon. The dragon set the carbuncle on fire, but the carbuncle killed it after it was dead. It suffocated, kind of like my adventurers did.
Wow. Put some of these in a cage as a surprise to invaders and you would be invincible.
*EDIT*
I then put one against an "Unarmed" rift warden. The rift warden beat him in a spectacular way. If they are immune, don't breath, or are just that tough remains a mystery.
So I put four of them against one unarmed, unskilled warden. The warden beat them easily, even though it is suggested that all four used the special that killed dragons in one hit. Wow. Fear the carbuncle plenty, but the wardens more...
*EDIT 2*
And against ten carbuncles it was no different. Taking the form of the warden, it would seem that he just ignores them.
So basically everything except rift wardens seem to die in carbuncle wind. Rift wardens you will have to find another way to kill.
*EDIT 3*
Tried against a hydra, and it died easily.
Upon actually taking a carbuncle over, it would seem I was wrong in thinking that it was the bladed air doing the damage, it was just the stated thing that happened around the same time. The actually attack was "Telekinetic asphyxiation", which seems easily capable of killing anything that needs to breath. This attack also has a high reload rate, so basically in a one-on-one fight, the carbuncle will win with most creatures no matter how strong they are. This also means the carbuncle is either going to win or going to lose, since if it's special works, then the enemy would die, and if it doesn't, the carbuncle would die. The dragon attack earlier was an acceptation, do to the fact that dragons have a range attack as well.