I have a Hidden Tide Turner and a Karne at my battlefield. My opponent attacks into the battlefield starting a showdown. I play Ride the Wind moving my Karne to base leaving the battlefield empty. Does my hidden card become discarded due to losing control of the battlefield? Or would I still have an opportunity to play the hidden card before the showdown ends? The old rules stated that you don't lose control of battlefields until the end of the showdown. But there's been some recent rules changes so I'm not sure if that's true anymore.

You do not lose control of the battlefield, and your hidden Tideturner is not discarded. You still have an opportunity to play it.

According to Rule 187.4.b, control of a battlefield cannot change while a combat or showdown is ongoing, regardless of whether you have units present. Per RiftJudge FAQ 715 and FAQ 6143, your battlefield remains "Contested" and controlled by you until the showdown fully resolves. Because the showdown is ongoing, the loss of your unit does not trigger an immediate loss of control, and your hidden card remains safe until the showdown concludes.

Sequence of Events:

1. Showdown Begins: Your opponent attacks your battlefield. The battlefield becomes Contested, and the game enters a Showdown state.
2. Playing Ride the Wind: You play Ride the Wind as an [Action] during the showdown to move your Kayn to your base.
3. Ongoing Control: Even though your battlefield is now empty, you maintain control of it because the showdown is still ongoing (Rule 187.4.b).
4. Using Hidden Tideturner: Because you still control the battlefield, you can still flip and play your hidden Tideturner as a [Reaction] to interact with the current state of the showdown (FAQ 6143).
5. Resolution: You only potentially lose control of the battlefield after the showdown has fully resolved (when combat damage is dealt and cleanup occurs).

This interpretation is based on the current Unleashed rules (Rule 187.4.b) and supported by specific interaction FAQs (FAQ 715, FAQ 6143).