An 8th day circumcision overrides a festival just as it does Shabbos, but its facilitators, like bringing the scalpel which could have been done before the festival, do not. Slaughtering the Paschal lamb or kid on the afternoon before Passover overrides Shabbos, but bringing the knife and sharpening it do not. Burning the leftover meat after the Seder is required, and kindling fire to cook meat is permitted on a holiday. Nevertheless we wait til the first intermediate day of Passover because burning the leftover meat does not contribute to our needs for the festival. A beautiful story about Shabbos and teshuva, atonement, from Rabbi Dr. Avraham Twerski about the Shpoler Zeide. Opening Mishna 2 of Chap 19 – the necessities of an 8th day circumcision (unlike the facilitators) do override Shabbos. i.e. the bandaging, ointment etc. Removing unnecessary shreds of skin constitutes beautifying the mitzvah and may be done on Shabbos as well, unless one interrupted the process.