Normally, when Mew transforms, it has 5 PP for a move.
In the actual game (not link battle or Pokesta), when Mew is given a Max Elixir/Ether/Whatever after being transformed, it fills up the number of PP for their old move. So let's say Originally, the Mew had Cut, Double Team, Softboiled, and Ice Beam. The Pokemon Mew transforms into has Horn Drill, Blizzard, Fire Blast, and Mega Kick for argument's sake. If you give Mew the Max elixir after getting these moves, Mew would have 30 Horn Drills, 20 Blizzards, 10 Fire Blasts, and 10 Mega Kicks, but it says for the PP, "30/5" for Horn Drill.
If someone's pointed this out already, I apologize for repeating.
Gundam Wing/Thundercats: WHAT'S THAT?!? Sword of Omens, give me sight beyond sight. I'm going to fight it. Thunder...thunder...Thundercats...(buster rifle to the head).