You may only enter this cave with all 8 Hoenn badges and have all the HMs. Also, aside from the all powerful continent and sea poke'mon here, there is another ancient being that resides here. May only enter from Sootopolis city.

Appearing Pokemon:

Roll one 6-sided di.
1=Zubat
2=Zubat
3=Golbat
4=Sableye
5=Zubat
6=Zubat

The level will be determined in the next post of battle by rolling 1 4-sided di again, however this time the corresponding number will be the level.
1=Lv. 27
2=Lv. 28
3=Lv. 29
4=Lv. 30
This may only be done every 5 posts in this cave.