I’m not sure if this applies to other Mythic skins, as I don’t own/use them as frequently. For Kiriko and Juno, however, there are occasional inconsistencies with specific voice lines. With Juno, sometimes her standard “one small step at a time” hero selection voiceline will play instead of her mythic-only “one magical step at a time.” With Kiriko, there is a more prominent one: she was given a mythic-only ultimate voice line (“let my sunlight guide you,”), but it only plays sometimes. Other times, you will hear the standard “kitsune” ultimate voice line.