1. For the cards I can play, do I have to play them or can I just discard them if I don't want to
2. Am I right in thinking the only two valid edict cards you can play at this time are timegash and plague. I presume rebirth can't be played because that is before a challenge starts.
Also, is it possible to target a planet with just my own cones on (to avoid attacking somebody)?
1. You don't have to play any cards. After Allies are committed, you discard your hand and get a fresh hand of 7 cards. (FFG version is 8 cards)
2. Timegash is only at the start of (any) player's turn. If the Offense has already flipped the destiny pile, then you cannot play Timegash. Not sure on Plague, I think it's at the start of a challenge? You could Cosmic Zap, I think . We always played that you could CZ any time during the turn, and the power was just gone for the rest of the challenge.
And you can target *any* planet in the color's system. If you have tokens on that planet, then you still have to attack, and if you win, you just add to the pile of tokens on that planet. You have to take one challenge on your turn, but you don't have to take your second challenge.
And almost all version of Cosmic Encounters are very similar, so most rules can be applied