National Dex/Completing The Shinou Dex:

Luckily, in this game, all you have to do to complete the Shinou Dex is SEE all the Pokemon in the Dex, as opposed to catching them like in previous games. And once you see all the Pokemon, you unlock the National Dex. There are 151 Pokemon in the Shinou Dex, but not all the new Pokemon are included in it.