I was pre-clearing an Act 2 Mp4 Key Warden run when I came across an elite pack + champ pack in the Sewers. The elite pack was Arcane Sentry / Fast / Fire Chains (I don't remember the last affix). The champ pack was Molten / Knockback / Teleporter.
Serenity was just coming off cooldown as I died. I originally tried to use the ladder as a quick escape route but I wasn't able to click on it, so I tried to survive long enough with LoH just long enough for Serenity. Maybe next time!