All I do is, Big Z lobs a nade to distract the rancor, Mission sneaks past to the platform, DOES NOT OPEN THE DOOR, shoots at rancor with most DPS-y ranged weapon/skill combo, get lead and Big Z up the corridor, then wait for several minutes as Mission (blue girl) blasts the freaking prick apart. If lead is leveled towards sneaking and has a cloak belt, could also take the lead to same platform and have them do it together, to take the freak down about 2x faster, but I wasn't a sneak type in my last walkthru.