Doctor Who: Every NuWho Companion Ranked From Worst To Best

For however briefly a time, Missy did indeed travel with The Doctor as a companion (though NEVER let her hear you using that term).

The growth that Missy displayed while in the TARDIS with The Doctor (or perhaps more accurately, in the Vault) was enormous. While never truly moving to the 'good' side, she certainly displayed a growing respect for why The Doctor acts the way he does. It may not have been a change that would show any true lasting impact on The Master, but this incarnation may best be remembered as the one that showed the most promise.

Missy's demise at the hands of her previous incarnation is a sad ending to what could have been an insane, twisting arc through the stars. Though Sacha Dhawan is now The Master, it remains to be seen just how much of Missy is left alive inside him.