yeah, what Follow said.
ONTO BERYL:
If you didn't save all the police, the police won't be hypnotized in the Gym, and you fight Corey in the Corrosive Field instead of the Corrosive Mist.
Tropius is available in the Jungle on sunny (or windy, I forgot) days. (nvm, to have to do a later event with the Nuzleaf.)
Helioptile can be found on the roof on sunny days. Pokesnax required to take it.
Big Root in Jungle, again, is optional.
After saving all the police, if you go back to the chief, he'll give you a Growlithe. You can trade this for an Azurill with one of the officers.
After Corey, if you go back to the Mansion in the Jungle, you can clean up the Mansion. After doing so, the Gothitelle will give you a Soul Candle, and you have the option of taking a Gothita with you.
At night, if you go to one of the pumpkins with the Soul Candle, Pumpkaboo will attack.
That's all I remember, for now.