On poke cup masterball (50-55) can someone tell me how to beat it. Can..

First, you should use Starmie. It's a good Pokemon in Pokemon stadium. Second, try to have a Pokemon of each type, and if you can choose a Pokemon with two different moves, like starmie which has a water and electrik move, that would be better. And to face electrik pokemons, you should have a rock or ground type pokemon. If the oppenent has a electrik Pokemon don't choose a rock or ground Pokemon to begin, start with another. Example: you choose a water Pokemon to begin and the opponent a electrik one. The opponent will choose a electrik move, of course, so choose to a rock or ground Pokemon type. So the electrik move won't effect him. Here is a list of Pokemon you should use to:

Ultraball: Fearow, Dugtrio, Kadabra, Dewdong, Starmie, Jolteon

Masterball: Sandlash, Kadabra, Gengar, Starmie, Electrode, Articuno.

Sorry but I don't ahve Poke and Greatball, I don't remember the pokemons. I hope this will help you.

I would suggest using Pokemon with moves that affect the Pokemon state (ex. Sleep powder makes the opponent fall asleep) it gives you more time to attack and weaken the opponent.

I used my own team of only Starme Rhydon Zapdos & executor. Starme has ice beam, thunderbolt, psychic, & surf. Rhydon has body slam, substitute, rock slide & earthquake. Zapdos has drill peck, thunderbolt, thunder wave & substitute. Executor has sleep powder, psychic, mega drain & explosion. Starme level 55. All others are 50.