Hidden Gibbons

It changes into a creature even if the spell is countered.

When it turns into a creature, it is no longer an enchantment.

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.

The ability triggers when the spell is cast, so it becomes a creature before the spell resolves.