I only know 1, Sliggoo. What exactly are they?
NFE stands for Not Fully Evolved. So these are all Pokémon who are not final evolutions. But some Pokémon, like Chansey, are in OU, because they are good in higher tiers because of the Eviolite, an item that increases the holders defence and special defence if it can still evolve.
I hope I helped!