Mime Jr.'s awful. Sorry. It just is. It has 30 HP, and the ONLY way you won't be OHKO'd is if you manage to stay asleep until your turn. That makes a 25% chance of even attacking the next turn without your opponent being able to. Now, most decks run about 20 Pokémon. About. So every time you attack, you have about a 30% chance of LZing a Pokémon. That means about a 7.5% chance of LZing a Pokémon without your opponent attacking Mime Jr., which will surely be OHKO'd. Besides, they can also snipe, Luring Flame, Bright Look, Reversal, Circulation, Warp Point, Cyclone Energy, etc. into another Pokémon. Mime Jr. was mediocre even for a Prerelease, and definitely is not a viable way of winning.