1. Using optimised evs on Pelipper:
The pelipper set you are using is slower than 16 speed Mega Venusaur which makes Pelipper eat a hit first and then attack so to remedy this, you should run 140 speed pelipper as it outspeeds 16 speed mega venusaur and can attack it first with Hurricane:
Pelipper @ Leftovers
Ability: Drizzle
EVs: 252 HP / 116 Def / 140 Spe
Bold Nature
IVs: 0 Atk
- Scald
- Hurricane
- Roost
- Defog
2. Since Rain teams are based around offense, you cannot
generally fit in defensive pokemon such as Empoleon and Mantine on them.as they take away momentum which is something offensive teams thrive on. ( Rain Balance is an archetype however the defensive mons need to be the right one's such as Empoleon + Toxapex) Regarding moveslots, you have 2 defog users and 2 stealth rock users which is imo a waste of slot.
I suggest you to use Choice Greninja over empoleon as Greninja with a scarf is a good speed control and checks pokemon such as Tapu bulu and Tapu Koko. Next up you should use Gyarados with Fly z to beat Poison teams better and use Choice Band on Azumarill to wallbreak. I have included a team with the changes suggested.
https://pokepast.es/7ccc26e0e64dd03d