The purpose of this setup is to cause drama and have people constantly backstab each other.
Yaks claim d1. Town has a choice, do they want to convince the yaks to yak them and joint win or try to win as town but feel the yaks' wrath?
If town tries to lynch yaks d1, the yaks simply yak those who lead the lynch to make them lose too.
So d1, town has to try to convince the yaks to yak them THEN backstab their townies so they can win as well. Yaks may ask for any incentive to yak the townies; karma, friendship, cheating partnerships, sexual favors, etc.