Hidden Gibbons

• WWizards of the Coast2004-10-04
  Official Ruling
  It changes into a creature even if the spell is countered.
• WWizards of the Coast2004-10-04
  Official Ruling
  When it turns into a creature, it is no longer an enchantment.
• WWizards of the Coast2008-08-01
  Official Ruling
  A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.
• WWizards of the Coast2008-08-01
  Official Ruling
  The ability triggers when the spell is cast, so it becomes a creature before the spell resolves.

Rulings via Scryfall