When you pick your two nemesis cards are you supposed to show them to the rebel players then or wait until you bust them out in a mission? If the latter are you supposed to tell them they are a nemesis?

You mean, do you show them the two villains you have selected?

Technically the Powerful Foes does not ask you to take the cards out and show them to the rebels, you only choose which villains you want earned. The first time you handle their deployment cards is when you select your open groups for the mission and choose to include either one of them, and open groups are by definition hidden information.

Which will be more fun for you and them?

Thanks. Well surprises are always fun. I guess I'm wondering when you "earn" something do the Rebel get to know? Sounds like no. In that case technically they will never know who the nemeses are (unless they know the missions well). But if they see Greedo three times they'll figure it out.

During missions the Imperial player reads the full text of events, except not reading any optional parts that were not chosen. In end of mission rewards and if another side mission was played instead of an agenda side mission, the text tells of an earned/gained villain. In the case of Powerful Foes the text does not say which villains are earned, and does not contain instructions to reveal the chosen villains. (Btw, Reveal is used as a mechanism now in the class cards, so read the paragraph from the campaign guide.)

I am not sure which way this is intended to be played, but this is a great place for a house rule, just like keeping the names of the chosen agenda sets secret.

(I.e. minimal effect to the play itself, but maximum effect for the feel and thematics.)

I think when I deploy one for the first time near the end of that mission I'll drop a not so subtle "You've not seen the last of me!" and they'll get it. I don't care if they know who the nemeses are but I'd rather it come out in a mission where they show up for drama/flair rather than before the first mission which is meta. So I think I'll keep it secret until then since that doesn't appear to violate any rule. Thanks for helping me think it through.