5 Classic Doctor Who Villains That Still Need To Make Their NuWho Debut

4. Sil

This creepy slug-like alien was part of a darker period of Doctor Who history during Colin Baker's tenure.

A gambler and con artist completely devoid of morality, the 6th Doctor had the misfortune to cross paths with Sil twice during his incarnation. The second time, the beast was partly responsible for the death of the Doctor's companion Peri, which makes it likely the Time Lord still has a score to settle with him.

He's not been seen in the main show since, but a reappearance would most certainly bring out a darker side of Jodie Whittaker, who would no doubt feel her companions would be threatened by this creature.