Does anything special happen if a Maerorus is made from a Magical Girl and her witch self? Higher/lower SAN than normal Maerorus? More powerful because synergy? Weaker because abilities are redundant? Different chance of successful operation? I’m asking because The 9th has Sayaka and her witch core.

Lower SAN in the sense that it makes them feel and see things they shouldn't be, like being look through the veil behind reality. Definitely more powerful. It's really a wild card.