I recently found a few of the Freeport sourcebooks at the local used book store. Bought them because I'd wanted to run the trilogy (Hadn't before because a friend kept on planning to run one and there have been issues in the local group with people who knew more about the setting than the DM so I'd avoided them before). The setting is D&D 3.5 using a few bits from UA and other house rules.
One of the players was looking through the City of Adventure book and noticed the sidebar about the unknown connection between the Yuan Ti and the Serpent people. The end result is a player wanting to play a Tainted One (From Savage Species, I'm allowing the player to sacrifice a 1st level feat to drop the LA thanks to another player going lesser aasimar with the Otherworldly feat and force both players to use a LA buyoff as if they retained it to get a feat though the Aasimar will lose the Otherworldly feat and switch to normal aasimar at that point) and I'm looking for anything to deal with how a yuan ti would deal with the serpent men and the other way around.
Only hint I saw towards Yuan Ti elsewhere in the various freeport supplements was a reference to a character in one of the books I don't have.