Can Sprite Call be revealed and played as a reaction to hard removal targeting the only unit on a battlefield where it was hidden?

Ruling: Yes, Sprite Call can be revealed and played as a reaction to the removal, allowing you to play the sprite to that battlefield.

Sequence:

• Conquer a battlefield with a single unit
• Hide Sprite Call
• Opponent plays hard removal on the unit
• Reveal Sprite Call as a reaction and play the sprite

Nuances:

• Hidden cards can be used as reactions starting the turn after they were hidden
• Face down cards gain reaction (they don't just act like they have reaction)