Amina Sinai née Mumtaz Aziz
Who shape shifts more than Saleem's mom? It could've been aunt Alia. It could have been Vanita, Wee Willie Winkie's wife. It could have even been Mumtaz Aziz, but she needed to change her name and become Amina Sinai to become Saleem's mom. There's a lot to say about Amina Sinai, but we know you don't have all day so we'll stick to the big stuff.
Shadeism. It's the prejudice against darker skinned people within a single race, and unfortunately it is not at all uncommon. We get to see this through Mumtaz, because she has much darker skin than your "typical" Kashmiri woman.
Mumtaz's mom doesn't like her. She describes her as "[...] the blackie whom she had never been able to love because of her skin of a South Indian fisherwoman [...]." (1.4.12). We guess she has a face that not even her own mother could love. Her dad, on the other hand, is a modern progressive man and he loves Mumtaz for what's on the inside.
Naseem isn't the only one who is shadist. Ahmed's cousin Zohra seems to have a habit of talking about how lighter skinned people are just naturally more awesome than darker skinned people. When she is exposed, she's all I totally didn't mean Amina (1.5.16). Oh yeah, we're sure. Totally.
Maybe it's because of the prejudice that she experiences that we see many of India's social injustices through Mumtaz/Amina. When she goes to Shri Ramram Seth, we learn about the slums of India for the first time and see the poor children whose legs have been broken so that they can beg better. Since Saleem's family is well off, this isn't a side of India that we see very much in the novel.
Later on, Mumtaz even joins in the fight against inequality and prejudice. When her long-lost lover turns out to be a communist leader, she goes with him to visit the poor and do charity work. Don't forget that she also stood against religious prejudice by protecting Lifafa Das from the anti-Hindu rioting mob.
Even Amina is not immune to prejudice, though. When Ahmed starts his fetish for the so-called Coca-Cola girls, she says that they have funny names in an obvious show of anti-Anglo (people of mixed English and Indian heritage) prejudice. Mary corrects her:
"They aren't so funny names, Madam; beg your pardon, but they are good Christian words." And Amina remembered Ahmed's cousin Zohra making fun of dark skin—and, falling over herself to apologize, tumbled into Zohra's mistake: "Oh, no no, Mary, how could you think I was making fun of you?" (2.9.39)
Sound familiar? Little does she know that her Saleem is an Anglo, too.
Not A Witch, But Just As Powerful
If you ignore the whole cheating thing, Amina Sinai is probably the most traditional example of a good wife in the whole novel. She's quiet, pretty (but not too pretty), loyal, long-suffering, and she knows how to support her family even when her husband can't without hurting his feelings. What more could you want? You know, aside from no adultery.
Amina, like her brother Hanif, is truly her father's daughter. Her dad fell in love with Naseem through the perforated sheet. She uses the same technique to make herself fall in love with her second husband. That's when we learn about her assiduity (that's just a fancy word for being obsessively attentive to everything). She moves all the furniture, changes all his clothes, and changes everything around in her house until she loves him. That's commitment, folks.
She likes rearranging furniture. Big whoop. Yeah big whoop, because all the women in this story, even the ones who are not magical like Parvati, use magic. Pia's magic was turning the world around her into a Bollywood movie. Amina's magic? Changing the world around her.
Amina uses her assiduity to recreate the happiest time in her life: her underground marriage to Nadir Khan. Saleem tells us:
Under the influence of a painstaking magic so obscure that Amina was probably unaware of working it, Ahmed Sinai found his hair thinning, and what was left becoming lank and greasy; he discovered that he was willing to let it grow until it began to worm over the tops of his ears. (1.5.13)
If that transformation isn't magical, we don't know what is.
Amina works this magic trick not once, but twice. After Ahmed has a heart attack, she uses her powers not just to restore him, but to make him better than he ever was. That's when they fall in love for the first time.
Can't Get Over Her Ex
Once upon a time there was a dark beautiful girl. There was also a guy who lived in her parents' basement. Everyday this beautiful girl took care of the guy in the basement, until one day they fell in love. They got married and lived in the basement until the girl's father figured out that she was still a virgin after years of being married. The guy ran away and divorced her. She spent the rest of her life, even after she got married again, thinking about him.
It's not exactly a fairytale, but that's the story of Nadir Khan and (then) Mumtaz Aziz. We probably hear a lot more about Amina and Nadir than any other couple, but their mismatched love is really just one example of how no one in the novel seems to be able to hook up properly. Parvati and Saleem don't work out, and neither do Amina and Ahmed, Naseem and Aadam Aziz, Pia and Hanif, or any of the other couples. The only people who seem to be an okay match are Padma and Saleem, and that marriage ends the same day that it begins.