HaleyhRuby

here, this one have Pokemon Learnset Display: and this one too: look for one that is better for you :)

here: and a recommendation:

This is strange, when I spoke to the guy at the help center, he told me that I needed to have finished both quests...

in Kakori village, in the help center there, at the table on the right is where you can get the rewards (that's if you've already done both the princess and the lighthouse quests)

in fact, yes you can. You will have to sign a contract with him and you will need 5 to 10 black prisms to do so. When you sign the first contact (which is standard in the game) you will start a quest and when you talk to him again, he will ask you for the prisms (I just don't remember the exact number) and then you will be able to change the difficulty. There are other contracts there, but if I'm not mistaken, the only one that doesn't need prisms is the difficulty one.

In addition to the Oval Stone, you also need her to have a high level of happiness, then she will evolve.