Millicent! Millicent is my favorite minor character. All that we read of her is that she puts Hermione in a headlock, and that she's a rather large and intimidating girl. Sounds like someone you'd want to have on your side for sure.

(in my headcanon, Millicent marries Roger Davies, Ravenclaw hearthrob and they have tons of babies and Millicent becomes a magical historian. Davies' secret is he likes the ladies curvy. It's why it didn't work out with Fleur.)

ses//slytherin