Well, you really love a challenge, don’t you? The Sluggish Slug VS the Crazy Pelican! Since someone already suggested Gastrodon, I’m going to speak for Peliper.
Here is my recommended moveset:
- Fly
- Surf
- Ice Beam/ Blizzard
- Roost
The way your team is designed now, you lack two key aspect of a good ingame team: Fly and Surf.
With Peliper, you can get both! However, its Attack is minimal, so I would not use Fly in battle. It also got the Defensive bulk to (maybe) survive a hit from Cynthia’s Garchomp and then revenge-kill it with ice Beam/Blizzard. Both have to be taught via TM so it is your choice. I would use Ice Beam since it is more reliable.
Roost is good, sweet, reliable recovery.
One mayor advantage Peliper have over Gastrodon is the Speed. It can outspeed anything on Berthas team with relative ease, and it provides a nice Flying type VS Aaron. Against the gym leaders, if fares slightly worse except for Gardenia.
Gastrodon on the other hand fairs better versus the rest of the E4, due to better overall bulk and Ground type. Since your Roserade already deals with Berth, Gastrodon can take down Flint with relative ease.
- Surf
- Mud Bomb
- Ice Beam/ Blizzard
- Recover
Overall, Gastrodons Ground type, overall better Stats and movepool makes it superior to Peliper, but as I said before, your team lack Fly, and honestly, you will have big problems with the E4 anyway. Bertha may not be a problem either way, but Aaron, Flint and primarily Lucien will give you a very difficult time as it is now. Might I suggest replacing Girafarig? It is a very weak Pokemon, and it has poor types. I would suggest using Staraptor instead.
A good moveset would be:
- Aerial Ace/Brave Bird
- Fly
- Close Combat
- Take Down/Endeavor
So my tip: Use Peliper if you don’t want to replace anything, use Staraptor and Gastrodon if you can bid Girafarig adieu. Hope it helped!