Mewtwo
Slowbro
Cloyster
Articuno
Zapdos
Jolteon
In my battle plan, I have two Psycics(great for ghosts), Mewtwo and
Slowbro, two Waters(for shattering any rock and ground type), Slowbro
and Cloyster, two Ice(for dragon and fire), Cloyster and Articuno, two
Flyers(for fighters), Articuno and Zapdos, and, last but not least,
two Electrics(exactly what's needed for those pesky waters), Zapdos
and Jolteon.
P.S. Jolteon is also very useful with Pin Missle and Double Kick, so
don't throw those moves away. Pin Missle is great against Psycics, and
Double Kick is an invaluable asset against those... those...
rocks....!!! ;P Blleagghh!
in a battle, my pokemon would be these "simple six:"