Super Smash Bros.

Sound Test:
Complete Bonus 1 Practice (Break the Targets) and Bonus 2 Practice (Board the Platforms) with all 12 characters.
The Sound Test is then unlocked.

Unlock order:
Each hidden character must first challenge you and then be defeated in the match that follows.
If you finish the 1-Player mode in 20 minutes or less, Captain Falcon is the one who challenges you, even if you also met the conditions for Jigglypuff or Ness.
Ness takes priority over Jigglypuff.

Mew:
Once you have unlocked any of the hidden characters, Mew can come out of a Poke Ball.

Change outfits:
On the character select screen, press any C Button to cycle through a fighter's four color schemes.
Press C-Up for the default outfit.

Camera swivel:
On a character profile screen, hold Z and move the Control Stick to rotate the camera around the character.

Borrow a life from a teammate:
In a Vs. mode team battle, after you have lost all your lives, press Start to take a stock life from a teammate who has at least two left.