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.
WARNING! VERY IMPORTANT! There are other Altars in the Den, but *only* the one at E-5 on the first map gives the Rancor Flame that you need to access the Sacrificial Chamber. If you trade your lanterns to the wrong Altar (the ones that give the Crimson Rancor or the Blue Rancor), without other players possessing lanterns lit with Rancor Flames to get through a separate gated area on Map 3, it will be impossible to get rid of the incorrect flame -- in this case, you'll need to drop your lit lanterns and farm new unlit ones.
It is recommended to clear this room because you can't light the lanterns while invisible, 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 have less than 4 people, you have time to go back to Altar of Rancor to get a new flames. Lights won't disappear.
If you get aggro after this, the entrance to the Sacrificial Chamber is a short run past the gate.
It should be noted that when all 4 lights are lit, the entrance to the Sacrificial Chamber only remains open for a few seconds. Afterwards, all 4 lights extinguish and the gate closes. Those who need to access the Sacrificial Chamber must pass through the entrance while the 4 lights are lit or risk having to relight them all over again.
After entering the Sacrificial Chamber, examine the Mahogany Door to enter the Battlefield.
The battlefield is capped at level 99 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 may 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 summons a random avatar for Astral Flow even if its elemental is asleep, so make sure your party is healed before waking it up. The maximum damage done by Astral Flow is approximately 700-800 without Shell or any sort of magical protection.
This fight can be completed solo by most jobs at 99 and is easily duoed. '(see testimonials)'
Clearing the battlefield gives a cutscene and places you in a different location from the entrance of the Sacrificial Chamber. Following this path leads back into Temple of Uggalepih away from the entrance to the Den.
After the cutscene you will obtain a Dark Fragment, for use in the next mission.