Level 48 Invulnerable/Fire Tanker
On any setting above Heroic the getting the keys to the side missions are next to impossible. Carnie bosses + Invulnerable Tanker = Dead Tanker ....... period.
I realize that at one time the Invulnerable powerset was way overpowered. But giving just about anything above level 40 that moves psionic attacks pretty much ends the fun of playing the game at level 40 for a Invulnerable.