Most covens in modern media, and even some not so modern media, usually depict three witches, sometimes based on the Maiden/Mother/Crone trifecta, but mostly based on the Weird Sisters in MacBeth. Some are also based on the concepts of the Norns in Norse mythology, or the Fates in Greek mythology, both groups composed of three individuals.
Either way, three seems to be a happy number for mystical witches and hags.
But we only have two here. Camille and Lissandra. On a personal note, it's been driving me crazy that there are only two,~~ but it also may give me a little more hope that the next champion may be the popularly theorized Ighilya from Ahri's Garden of Forgetting Story - the old woman known as the Forgotten, the Eater of Secrets, and the Witch Gardener. The lack of a third coven skin gives me hope that the next champion will be her, and bring the third coven skin as her launch skin.~~
What do you guys think?