We arrived at Kel'Thuzad, the penultimate boss of the raid. We had ideas that the fight would be the hardest so far, but we soon realised that wasn't the case. We wiped a few times, as you do, on messing up mechanics. And we felt the hurt in the very last phase of the fight. But soon enough we managed to kill Kel'thuzad the 4 times the encounter required! Nine bosses down and only Sylvanas left!