Marriland team builder
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It's a really great site for things like this!
I put in your team and it seams very well rounded!
Two of your pokemon are weak to water but since your Vaporeon has Water Absorb it should be no problem.
Another two are weak to grass, but Ninetails should easily be able to reduce that threat (And Hitmonchan offers great backup with either Firepunch or Icepunch should Ninetails get eliminated).
Vaporeons electric weakness is negated by Sandslash electric immunity.
Sandslashes ice weakness is handled by Scizor, Vaporeon and Ninetails resistances towards it.
Ninetails doesn't like ground but a Surf from Vaporeon would pose a considerable threat to any ground pokemon, as would an Icepunch from Hitmonchan.
Flying hurts Hitmonchan, but Icepunch hurts most flying pokemon in return. And Firepunch hurts Skarmory a bit. It's physical though, so don't expect to out perform Skarmory with only Hitmonchan, Ninetails would need to pitch in with some special firepower.
Hitmonchan should avoid psychic attacks aswell, but a Technician supported Pursuit or a Swarm supported X-scissor would most likely eliminated the threat right then and there.
Ninetails should naturally stay clear of rock type attacks, while Hitmonchan, Sandslash and maybe even Vaporeon handles those, nothing to worry about here.
All in all I think your teams is very well rounded typewise, both defensively and offensively. Perhaps you should simply go for a pokemon that offers some valuable utility. Some great team supporting attacks and the likes. Since I don't know what your pokemons attacks are I can't make an informed suggestion but I think you should just go with one that's fun anyway. And since your team is so well rounded you could easily try alot of different utility and support pokemon effectively!
Hope this helps
