My PCs are charged with uncovering a cult's motives, however they will engage a deadly encounter which lead them (unknowingly) to a troll city.
I thought it would be intresting to include a social combat challenge once they get there, where the PCs try to convince the troll leader to spare their lives in exchange for information.
In order to insert some drama and uncertainty I thought up the following mechanic.
The PCs are in wooden cages and below there's fire. The troll leader along with a shaman are in front of them, interrogating them.
At each question, the troll leader turn pulls a lever and 1 cage drops a notch closer to fire.
How do I implement mechanics to make this combat challenging and fair to all PCs?