Hi! I just have a few suggestions.
First, Blastoise looks like a cool stall mon, but if you have a drizzle setter rain dish is a better ability to make it last longer. You could also shift so EVs from Sp. Atk to HP if you wanted to make it even more bulky.
Next, politoed doesn’t have the offensive stats to justify running choice scarf on it, so if I were you I’d change it to a support Pelipper. It gets defog as well, so it’s a great support Pokémon. Give it a damp rock to make rain last longer. Roost allows you to be able to stick around and set more rain, and slow u-turn let’s your sweepers come in for free.
Pelipper @ Damp Rock
EVs: 248 HP / 252 Def / 8 SpA
Gyarados and vaporeon look good, but I’d give gyarados a life orb to make it hit harder.
Tentacruel also looks solid, but I’d give it rain dish instead of liquid ooze, and scald is probably better than hydro pump as well because of better accuracy and chance to burn.
Most people run special kingdra, but why not psychical? It has the same offensive stats, after all. I’d just change flail to flip turn.
Hope I helped!