1.- Can I enhance with Bitter Rivals even if i have no cards in my hand?

2.- When is a Card considered to be played?

1) yes. You always have a hand. When you reveal it, there are no cards in it.

2) after the control check has been passed, and all costs associated with playing the card has been paid.

i´m not according with de cost of bitter rivals, if you haven´t cards in hand, you can´t reveal nothing, then, costs aren´t paids.

Darkon01 said:

Sure you can. Maybe there is not much to see...but you can easily reveal every card in your hand.

If language isn't your first language (or even if it is) it can be a tricky language, and you have to understand the rules are what the words say not what they mean, lol.

Now if it said discard 1 momentum, you can't. However, if a card cost was "discard your entire momentum" it is playable with zero momentum (unless of course it states "only playable if you have at least one momentum")