Looks like their name may begin with N, they're between Nocturne and Nunu and Willump.
If you look at Champion Collection, you'll find there's a "None" empty slot. Clicking on it will take you to it's "champion page".
You'll see they apparently do Magic damage, they're easy to play, and they're an auto attacker. Is this the new non-traditional marksman?
Nothing else has been added as far as I'm aware, and I'm 80% sure this was done as a mistake.