Mew

Mew (Japanese: ミュウ, Myū) is a fictional creature in the Pokémon media franchise. It has appeared as a very rare Pokémon in each Smash-game, and the rarity depends on the number of revealed Pokémon during each games release; 1/151 in Smash Bros., 1/251 in Melee, and 1/493 in Brawl.

Creature description
Mew takes the appearance of a small pink feline-like sprite, which is endowed with legendary powers. In-game Pokédex entries describe it as a mythical Pokémon of South America that was thought to have been extinct until recently. It is so rare, it is still said to be a mirage by many experts; only a few people have seen it worldwide. Apparently, it only appears to those people who are pure of heart and have a strong desire to see it. It is very intelligent and is capable of any battle technique; for this reason many scientists believe Mew to be an ancestor to all Pokémon, and is thought to possess the genetic composition of every Pokémon specie. It is capable of making itself invisible at will, so it entirely avoids notice even if it approaches people. When viewed through a microscope, its short, fine, delicate hair can be seen. It is the subject of much research.

In the anime, Mew travels in a bubble, which is reflected in its appearances in all of the Smash Bros. games. Sparkles come out of the bubble while it moves around.

As a Poké Ball Pokémon
Mew makes its first appearance in Super Smash Bros.. It doesn't attack, but will instead remain on the screen for a few seconds, then fly off. It can be completely unnoticed when it comes out of a Poké Ball if the fighting is intense, since it doesn't harm anyone. Mew's appearance is rare since it is a legendary Pokémon. The summoner of Mew is awarded the Mew Catcher, worth 10,000 points. Mew has a 1-in-151 chance of appearing in this game. 151 happens to be the total number of Pokémon at the time when Smash Bros came out.

As a Poké Ball Pokémon
Mew reappears in Super Smash Bros. Melee, again flying off instead of attacking. The only difference in the "attack" is that Mew appears in it's bubble. No character is harmed by Mew's "attack" in Melee either, however it is said that if a player touches it's bubble, he/she will be bounced back, becoming a instant KO, although this isn't true. Mew can only be seen if all characters are unlocked. This makes Mew one of only two unlockable Pokémon in Melee, the other being Celebi. Both have a 1-in-251 chance of appearing in this game. 251 happens to be the total number of Pokémon at the time when ''Melee '' came out.

As a trophy
Mew is featured as a collectible trophy; this trophy must be specifically earned in melee by playing Hard or Very Hard in All-Star Mode to unlock the trophy. Continuing is allowed to get this trophy.

In ''Super Smash Bros. Brawl
Mew returns yet again in the third installment. This time though, it drops a CD. It is the rarest of all the Pokemon. After the first time you see it you will get a notice saying that it was your first time (like in Melee).

Mew appears at a rate of 1/493. 493 happens to be the total number of Pokémon as of Diamond and Pearl, including Arceus, who hadn't even officially been revealed by Nintendo yet when Brawl came out.

If you have collected all of the CDs, Mew will drop stickers instead, like Jirachi.