Super Smash Bros. Brawl/Pokémon

Bellossom
Bellossom puts nearby opponents to sleep with Sleep Powder.

Bonsly
Bonsly will use Tackle. But before that you have some time to pick it up and throw it. You won't be able to throw it quite far but if you hit someone you will damage your opponent a lot, even if your opponent has less than 50% damage you may be able to knock the enemy off the screen. Be careful though, as it overshoots more than expected.

Celebi
Celebi will release trophies to add to your collection.

Chikorita
Chikorita will use Razor Leaf as in Super Smash Bros. Melee.

Deoxys
Deoxys's act is similar to the one of Ho-oh in Super Smash Bros. Melee. It will float over the stage and unleash a powerful Hyper Beam (instead of Ho-oh's Sacred Fire.)

Electrode
Electrode uses Explosion. One modification they've made in this pokémon is that it might not burst when released. It can be picked up and thrown, though this is a bit on the dangerous side, as it can explode in your hands.

Entei
Entei will use Fire Spin to trap opponents into a fire vortex.

Gardevoir
Gardevoir uses Barrier. It makes a big circular shield around itself that doesn't allow blasts of laser guns and stuff like that to penetrate (it reflects them back), but it does allow enemies to enter and attack from the inside.

Goldeen
Goldeen does not do anything.

Groudon
Groudon stands on the stage and burns anyone who touches it with Overheat. This is usually a 1-hit KO, and it takes up a large portion of the stage, too.

Gulpin
Gulpin will swallow an enemy with Stockpile and chomp on him. Also, if the character swallowed hasn't escaped, Gulpin will spit him with Spit Up. Note: You can add damage while he's swallowed

Ho-Oh
Ho-Oh will fly behind the stage and use Sacred Fire, throwing a column of fire on the stage.

Jirachi
Jirachi is so rare that when you release it, it will drop stickers.

Kyogre
Kyogre uses Spout, a move that doesn't cause any kind of damage but that pushes the enemies off the screen with incredible force. The only way to inflict damage with Kyogre is if anyone comes into contact with it.

Latios & Latias
They both use Aerial Ace to knock enemies off the stage. This is quite effective, especially if your foe has just been lauched into the air and is vulnerable.

Lugia
Lugia will fly behind the stage and use Aeroblast. The Aeroblast will aim where the person who released it is standing.

Manaphy
Manaphy uses Heart Swap, an attack that makes two players switch control between the characters they chose. Don't try to commit suicide while controlling your opponent's character because it will count as a self-destruct. You will eventually regain control of the character you chose, so don't worry.

Meowth
Meowth uses Pay Day, firing coins in the direction the most characters are in relation to Meowth. This is useful as a way to Smash Attack players stuck in the jet of coins.

Metagross
Metagross uses a combination between Earthquake and Stomp. With Earthquake it buries the enemies in the ground and with Stomp it launches them away. You can also receive damage on first-story platforms.

Mew
Mew will probably do nothing as in SSBM, but it is so rare that when you release it, it will drop CDs.

Moltres
Moltres uses Overheat as Groudon. If you touch it you'll burn.

Munchlax
When Munchlax appears on the stage, it will slowly walk around, eating any item it encounters on the stage, including valuable ones like CDs. The moves it uses are Stockpile and Swallow. This can be annoying, but it can eat bombs without making them blow up which is good at least.

Piplup
Piplup uses a Surf move to wash away competitors on the stage.

Snorlax
Snorlax will again fall from the sky with Body Slam and crush competitors as he did in Super Smash Bros. Melee.

Staryu
Staryu will chase one opponent and start firing the move Swift at the enemy chased.

Suicune
Suicune will now use Aurora Beam. After a short pause, a narrow beam of light will jolt forward and disappear. Contact with the beam is generally a one-hit KO. It can be easy to dodge, however, as the beam is concentrated in a straight line. An enemy touching Suicune will freeze.

Togepi
Togepi uses Metronome, allowing it to use one of a variety of moves. Maybe the screen will become dark, making you unable to see the battle for a moment, or maybe it will put a flower on top of the head of some enemy nearby, taking some damage. Togepi can also momentarily burn nearby enemies or freeze them.

Torchic
Torchic will use Blaze. It will stand stationary with a circular field of flames around its body. Contact with the flames will pull the opponent in and cause constant damage. Just before Torchic disappears, it will shoot opponents out of the flames with decent strength.

Weavile
It uses False Swipe by quickly dashing back and forth between two points on the ground. Enemy contact with Weavile will cause the enemy to take 1% damage and suffer the same effect as a broken shield. In this state, Weavile continues to deal 1% damage with each touch until it disappears.

Wobbuffet
Uses Counter; if you hit it, it will become agitated, hitting anyone who comes closer. The length and power of this depends on just how hard it was hit. Be careful – it damages everybody, including the thrower of the Poké Ball.