Discovering there's a member of the McGonagall family who would be part of the Marauders gen was wild. M.G. McGonagall was a Gryffindor quidditch player during 1971, and has a trophy, and is likely a seeker. We don't know what gender they were, but I've decided woman because women. She's likely either Malcolm's or Robert Jr.'s, since she's definitely not Minerva's, so this is Minnie's niece. I named her Marcella Gwendolyn McGonagall and put her seven years above the Marauders, just to make the trophy something she got during her final year. This did result in her being the same age as Lucius and around the same age as the Black sisters, Prewett siblings, Weasley siblings, Lestrange brothers etc., so do with that what you will, I don't know when you headcanon everyone else to have been born.