If Blue Teemo is revealed before he becomes a defender, does he activate twice?

Ruling: Blue Teemo only activates when he becomes defender. The card was errata'd.

Nuances:

• A unit is considered "Defending" the moment it enters into a Showdown, whether at the beginning or later on
• If you flip Teemo - Strategist up from Hidden during an opponent's showdown, he will become a Defender and his ability will trigger