Ido Transformation

Ido Transformation (イド変化, id Henge) is a heightened transformation available to users of the Nenmu kekkei genkai.

Overview
Due to harboring a darker soul along their soul, a Kurama Clan user, while under the control of this dark side (or by will once mastered) transform into the demonic form of what resides with them. This triggers a monstrous transformation in the user's form, becoming a humanoid demon. This allows them to gain the attributes of the form's power and the enhancements. This form's main power though, allows for the increase in the power of the genjutsu cast. However usually those who achieve this form are being overpowered and the demon is using the power for evil. But for those who can master their full powers, this form becomes a valuable asset to them, serving a boost in their overall capabilities, similar to a Tailed Beast Mode (except somewhat weaker in strength).

Trivia

 * This idea was based on collaboration between Kami and Chix on the Kurama's Clan Kekkei Genkai.