Also for anyone looking for the hidden Pokémon, I'll leave a few vague hints.
1 - There is a restless grave in the cemetery. This one is probably the one everyone will find first.
2 - A peculiar plant may be more than it seems.
3 - Treat yourself to a little love. Now where are you going to find something like that?
4 - Found a mysterious code somewhere? Try typing it out!
5 - One part of the Settings menu looks like it can be used to write a code as well! Now, what's the Dex number of a Pokémon associated with that part?