I still haven’t worked out why you were fighting him, but Tevruden would probably be one of the middle bosses. He’s either a gear check, or a mechanics check. It’s a test so he’s more difficult to complete than the bosses before or after him.

As for his mechanics:

  • The tank swap was that Tevruden put blood plague/frost fever on the guy tanking him and you had to make sure that you switched tanks before he cast pestilence on his current target, inducing massive raid-wide damage if you don’t.
  • At 1% he deems the raid ‘worthy’, death pacts to 50%, and lets them pass on to the next boss.
  • Vengeance was his soft enrage. Eventually his damage would just get so ridiculous it would become unhealable.
  • Tev’s hard enrage would be him raising all of the dead people in the raid as his undead minions, who then start DPSing their former raid members and healing him (like what Arthas uses in ICC, but the spell completes.)