Viscidus – A Deformation on Ice

A special mention goes to the deformation Viscidus from the raid Temple of Ahn’Qiraj. This oversized slime blob was only an optional boss but gained a reputation as the most hated opponent. Nowadays, it drops a pet, which is why many collectors still go to the temple to obtain the little critter.
Viscidus not only dealt a lot of damage back then but also had an additional, really weird mechanic: it could not die in a normal way. When its health points dropped to 1, it continued to fight bravely!
The trick was to cover it with a lot of frost effects so that it slowly freezes. While frozen, you had to deal as many hits as possible to make “the ice break” and ultimately finish off the boss.
Those who didn’t have enough frost mages or shamans back then found this boss simply impossible.

By the way, nowadays the boss can be frozen using the Endothermic Blaster from the Winter Veil festival – much to the relief of all involved.
Fun Fact: Shadow Priests could destroy the boss for a long time with “Mind Spike”. Because it caused not shadow damage but “shadow frost damage” – a quirky idea from Blizzard that gave some spells two damage types (like Frostfire Bolt from the Mage).
What absurd or crazy boss mechanics do you still remember that thankfully no longer exist?