I used the smoke powder pouches I found in the hidden room. They (stupidly) leave a burning surface (what does burn, the stone?), it may be really as simple as that that Nere becomes hostile if he touches the fire. Maybe I was just lucky the second trial. As the game hints at using smoke powder to free Nere, Larian should take care that it's use cannot foul the quest. I will use bombs in the future (which are seemingly filled with inflammable smoke powder).
I don't know much about actual D&D... but the masks of maskmen can already be found in the game. They're part of the same faction as the hellbeast. They buff your strength when multiple people wear one nearby. I forgot what the forces are actually called when passing a history check. They're an elite force, though.
