Destroy the two statues in Temple of Thulian Might and Temple of Thulian Power to be able to kill Sarinich (Advanced Solo).
When Sarinich is killed the teleporters to the 2nd level open up, the zone reuse timer is set and the collection shinies spawn.
Kill Baroddas (Advanced Solo) to open up the door to the 3rd level.
Kill Phobis (Advanced Solo) to open up the door to the waterfall.
Swim down the waterfall. Kill all "a pained wretch" mobs in forest before engaging Venekor. He will summon all surviving "a pained wretch" mobs to him.