Idun's pre Epic version are all useless, practically a high countdown wall with low health. After that point, it becomes a creature that can heal all your Outsiders (Planes creatures) thanks to its Regeneration Aura: Planes, making it valuable in Outsider heavy decks. When it dies, it transforms into a weak wall which deals Holy damage to its killer and possesses Inspiration.
Regeneration 2: Plane
Regeneration 3: Plane
*NOTE: Fields that contain the text *See above means the effect remains the same until said otherwise.