imo (just off the top of my head)
El Dorado, Wolf remix for EXO as a whole
and individually
Drunken Truth, Stained, Tears for Chen
Really I Didn't Know for chenbaek
Moonlight for Chen and baeksoo
Tell Me What is Love for Kyungsoo (idk if there was a live performance of this though)
these songs all seem harder to sing but idk much about vocal technique so kaowjdoiajwosawds
but Drunken Truth and Really I Didn't Know are DEFINITELY harder