I just watched Number Lore | 5, and it was insane I won't do any spoilers, this is the official Silhouette of 6. Make your Predictions! (Go down to see what my prediction of Six can do.) I think 6 will be a Purple Poisonous Lizard who can go invisible, and she can mind control a Letter. But only one at a time she will control the strong letters to her advantage, the only way to stop 6 from Mind controlling is to knock her out without getting bit by her poisonous substance in order for the 6's mind controlled to stop. Her poisonous substance can sometimes be fatal to some letters who are weak the strong ones will just get dazed.
Credits to Mike Salcedo & Number Lore. Please don't make your design similar than mine please.