What is a Tos quest?
The Tavern of Spear crossover quest... It's the one with the misty abyss and the chief of the lizard's tribe from Tavern of Spear (I think his names is Nexaus. The actual name for the quest is called ''Between worlds''. I think it was added some time around v0.19. After finishing up that quest you have the nightmares.
You need to finish the lizard questline first. Then you have to look through the dark swamp until the character from ToS appears. When he appears you will be in a new area called ''Misty Abyss''. Then he will show up at the lizard's temple with his questline. (I don't want to spoil anything - personally I think it's well written and worth to go through)