I love everything except the ult.
And it's not that the ult is bad at all, just that there's a lot more you could do with a mime. Every moba has a copy character, and IMO such an ability would be more fitting in many other designs. It's vaguely on theme, but imo its giving more shapeshifter, thief, supernatural spirit, etc.
For example, instead of copying all their abilities, levels and items, what if the person you copy receieves a portion of all the damage you take during the ult?...