what is this "Scary Warning" it says the exp will change. what does that mean will it be something really big or minor? please help me i really wanna know.

I don't know where it says " Scary Warning " but yes the exp gain formula will change.
Right now the exp you get is your opponent's level ^1.7. But after the exp change you will gain less experience from the opponent, meaning you will need to do more battles to level up. It might be something like opponent's level ^1.65, that's not decided yet.
The first levels will not be much harder, but the higher your pokemon gets, the harder will be the leveling.

Thanks but just so you know its on the home page, its the last part before it says thank, Da Man.