Impa has a lot more potential outside of just a clone. She is seen with a blade in OoT and uses lots of weaponry in Hyrule Warriors. She is the shadow sage in OoT and is a sage in ALBW as well which could pull some influence on her moves. She could have something similar to Sheik's recovery but she throws down a deku nut before she disappears stunning those in the area. Her down B could be that magic shield she uses to protect Zelda from Ghirahim in SS. Her side special could be a side sweeping attack where she dashes quickly across the stage with a blade out similar to Fox's just not quite as fast or large of a range but with more power.
I don't disagree with any of that, I was just responding to the topic. I wouldn't mind if Impa did show up on the roster as a clone of Shiek, perhaps with more shadowy properties involved in her moves since Shiek already takes a fair bit of inspiration from her. I'd love to see her as a fully fleshed out character too, but I wouldn't be offended if she weren't, especially since a lot of her incarnations can vary pretty wildly and it might be deemed not worth it to grab moves from all her different variations.