If a hidden Tideturner is at a battlefield and the only other unit there is moved away by Blitzcrank, can Tideturner be revealed and played to swap with the moved unit before being discarded for losing battlefield control?

Ruling: No, there is no window to use Tideturner's effect to save the unit being pulled. You can flip Tideturner but it will have basically no useful effect.

Nuances:

• This differs from the contested battlefield scenario where you can Fight or Flight a unit to base then reveal Tideturner to swap with it, because in contested situations hidden cards aren't removed until after the showdown completes during the next cleanup
• When a battlefield is not contested and you have no units there, you lose control immediately with no window for hidden card abilities
• You can still flip the Tideturner rather than losing it for nothing, but it won't achieve the desired swap effect