Hi again my friend!
I'm back from a 4-days trip to a faraway place where the rivers abounds.
However, i'm here to rate your team once again...
Yup, as @Episode36 said, once Gastro is dead, a powerful water-type move boosted by rain can kill all your team. The first pokemon that i can see doing this is Keldeo.
Choice specs keldeo can spam hydro pump and destroy you, however, he is not invincible.
Amoongus. Yes, Amoongus. He can take every water type move without making an effort, also he can spore and neutralize every pokemon.
Sub Calm Mind Keldeo? Ha. Not a problem, run clear smog on Amoongus and all stats-boosts on the little pony are gone.
Now, I don't hate gengar, but i never use it because of his frailness, he is OHKO'ed by a lot of moves, so replacing him with Amoongus is a great idea (i think so).
Try this changes and then tell me about what happened, your friend...
"Hax is actually the game deity teaching us the value of effort and humility, and, without it; we will be just playing another chess game. If somebody EVER haxes you and says he embraces it, just chill, take the nearest glass and break it, and remember: they're only dick-riders."