Being more lenient regarding Shabbat than Yom Tov, because Yom Tov is inherently more lenient in its laws, leading people to possibly disregard its prohibitions: Beitzah 2a-b
Prohibiting movement of an item which has a permitted use on Holidays, if it is not a movable vessel on Shabbat: Shabbat 124a
Permitting Work with an Altered Form: Shabbat 117b, 128b, 148a, Pesachim 47b
Violation of a Rabbinic Prohibition for that Holiday, or for the following Shabbat, is permitted, but not fora "Distant" Use: Shabbat 114b, Pesachim 47a
Breaking one rabbinic prohibition to announce that another one is permitted: Shabbat 114b
Building a temporary rooved structure, such as by adding shutters to a roadside stand: Shabbat 125b, 137b-138a; Eruvin 44a-b; Beitzah 10a, 11b-12a
Adding on to a temporary rooved structure, such as by removing shutters from a roadside stand: Shabbat 125b, 137b-138a; Eruvin 44a-b; Succah 27b-28a; Beitzah 10a, 11b-12a