sourceIMDB Craft Trivia wrote:An official website of the film said: "The crew had to return to the location a second time to complete filming interrupted by several weird occurrences that even caused witch consultant Pat Devin to raise an eyebrow. As the fog rolled in at midnight, the four actresses used actual Wiccan rites and language to invoke powerful forces. Then, as Fairuza Balk's character Nancy attempts to invoke the deity Manon, a flock of bats hovered over the set and the tide rose dramatically, extinguishing the circle of candles. Witchcraft consultant Devin recalls that 'Manon, a fictitious creation for the film, sounds very close to Mananan, the Gaelic god of the sea. Luckily, we weren't all swept to sea!'" Director Andrew Fleming is quoted: "'Every time the girls started the ceremony, and only when they would start the ceremony, the waves would start coming up tremendously fast, pounding heavily. Then, right when Nancy says her line, "Manon, fill me," right at that exact moment, we lost power. It was a very strange thing.'"
So the power of the rites was there even if it was to a fictional God. Though I did wonder about the name Manon as it does sound a lot like the god Mananan and given that they were doing the rites at the ocean...Hmmm....