Make a team that contains 3 of the following pokemon:

Snorlax lvl.55 Moves: Rest, Body slam, belly drum and snore. item:leftovers.
Umbreon lvl.50 Moves: Confuse ray, faint attack, psychic and mean look.
Item: Gold berry.
Starmie lvl.50 Moves: Blizzard, thunderbolt, surf and psychic. item:Focus band.

With these 3 pokemon you will surely be invincible, believe me I completed masterball-round2 with 5 continues.