Go to another entrance into the temple at (J-9) in Yhoator Jungle.
Once in the temple, go to (H-7). There should be (2-3) Tonberry Maledictors there.
Alternatively, enter the Den of Rancor from Yhoator Jungle (J-7). Be careful not to fall through the hole as you sneak southeast to (J-9) and enter the Temple of Uggalepih. You can camp safely on the stairs here, and there are Maledictors nearby.
It is recommended to clear this room because you can't light the lanterns while invisble, or getting hit.
To open the gate, have each person with a Rancor Flame light one of the four lanterns by trading their Rancor Flame to it. You will still have the Unlit Lantern after using the Rancor Flame, in case you need to help other people at another time.
If you have more than six people going through this, keep in mind that the gate can be opened from the inside by having someone to target the switch and press it.
If you do get aggro after this, the entrance to the Sacrificial Chamber is a short run past the gate.
After entering the Sacrificial Chamber, examine the heavy door to enter the Battlefield.
The Battlefield is capped at level 90 and limited to six players. Buffs wear upon entry (including Reraise), but Experience Points are not lost.
There are three Tonberry NMs. All three must be defeated to clear the battlfield. The recommended order in which to kill them is:
The Thief is completely immune to sleep, so you'll probably want to kill it while you Silence and/or Sleep the other two NMs.
The Summoner comes with a pet; a fire, water, or light elemental, chosen at random. It dies when its master does, so it need not be killed. The element of the pet is not an indication of which Astral Flow the Summoner will choose to use later in the fight.
At approximately 25% HP, the Thief will attempt to use Everyone's Rancor. The person this hits is liable to be K.O.'d in one shot if they have not recently reset their Tonberry hate.
The Summoner will summon a random avatar for Astral Flow even if its elemental pet is asleep, so make sure your party is healed up before waking it up. The maximum damage done by Astral Flow is approximately 700-800 without Shell or any sort of magical protection.
On clearing the Battlefield, you will receive a cutscene and exit in a different location to the entrance. Following this path leads back into Temple of Uggalepih away from the entrance to the Den.
This fight can be completed solo by some jobs and is easily Trioable with two DD's and someone who can sleep/heal/buff. (see testimonials)