Eliyahu will precede the Messiah by a day: Eruvin 43a-b
Eliyahu proceeding to the Great Court in Jerusalem first: Eruvin 43b
The Messiah from David, the Messiah from Joseph, Eliyahu and Shem ["The Righteous Kohen"] as the 4 foundations of the Redemption: Succah 52b
Relying on Eliyahu to determine the status of objects of disputed ownership: Bava Metzia 3a, 28a, 37a
Eliyahu revealing whether fish-skin may be used for Phylacteries: Shabbat 108a
Eliyahu revealing status of Terumah which is of uncertain Purity: Pesachim 13a, 34a
Eliyahu revealing status of Unidentified Legal Documents: Bava Metzia 20a
Eliyahu will not come on Friday or the day before a Holiday, because we need the time to spend preparing for the Shabbat/Holiday: Eruvin 43a-b; Pesachim 13a