This thread has the answer: Originally someone thought it was an exploit, however most people seem to think it’s not. It revolves around spots in the lava where you don’t take damage.
Get your whole team down there. Tanks and dps in front, then ranged, then healers and bauble-carrier. Enemy comes down, they’ve more than likely been splashed by lava so they are easy kills. If not, they get a knockback into the lava.
With one or two healers and a Black Orc/Ironbreaker who picks up the bauble after the Maurauder/White Lion, you can keep the bauble indefinitely and force the other side to come down to you. If you don’t have a Black Orc or Ironbreaker (unlikely), you can switch off with DPS and Healers.
Meanwhile you have one guy stay near the bauble spawn just in case this happens. If the other team gets itself together and a huge force comes down, make sure they are all down there, then everyone on your team suicides in the lava (yes even the bauble carrier). Then the attacking team is stuck down there with no recourse but to jump into the lava too. When the bauble spawns, the person who has been waiting, grabs it. If the other team has mostly suicided in the lava to respawn (usually 2-4 stay behind to stop your team from using the tactic again) get your ranged to mop up whoever’s left down there and send your tanks in with healers and wipe them out of there, then bring your bauble carrier down again and rinse-wash-repeat.
This strategy is proven to work if you do it right.