For the Master-of-Shapes mythic path from Mythic Paths of the Lost Spheres:
Mimic Greatness (Mythic)
Your assumption of the forms even legendary creatures is more complete.
Prerequisites: Moment of Supernature mythic path ability.
Benefit: You may select one 1st tier mythic ability from a path available to a creature you are currently mimicking with a shapechanging effect. You gain access to that path ability for the duration of the shapechange. Its effects resolve off of your tier or the original creatures, whichever is lower using your own levels and other statistics.