Question: pokemon ultra sun and moon how to get diancie?
Answer: There is currently no way to get a Diancie without transferring it up from XY/ORAS or trading with someone directly. If you happen to have one in a 6th gen game already, get Pokemon Bank and you can transfer the Diancie that way. If you don't, try posting on the trade boards and see if anyone is willing to do a trade.