I'd like to go into Barely Survivor's Returnee twists (particularly the Hole) and what each of them were, what mechanics they introduced, and why they worked so well to me:
The Hole had 6 people in it from start to finish and started with a double-elimination round. This was both to keep numbers at 6, and to force communication. I think this worked about as well as it could have, given we just thrust 6 people into a secret tribe. It was very likely that someone would get in the crossfire, so there was a little bit of playing the people who were on the other side of the vote to be favourable to you. This basically worked as well as I could have wanted it to, everything considered.
But the real shining star here is
I also really liked being able to insert an outcast tribe into the game as well for a few rounds. It gave people a hint of "what to expect going forward", and then dumping all of them off into a Shipwreck ensured that a few of them would survive into new tribes and also make sure they had a chance to properly meet EVERYONE, so they couldn't be singled out easily for not talking to people.
I don't think it was any specific singular mechanic that made the Hole a particularly amazing RI, but how they all worked together to make RI less of a problematic process by removing as many faults as possible while buffing its strengths.