From the Super Mario Wiki
PictoChat is a chat service found on the Nintendo DS. It is used to allow visual communication between up to 16 Nintendo DS handheld gaming devices at once.
 Using PictoChat
PictoChat is divided into 4 "chatrooms" marked "A," "B," "C," and "D" respectively. The maximum capacity for these chatrooms is 16. Upon entering a chatroom, users are presented with some very simple formatting options for drawing. The interface also contains a keyboard, which is able to produce a variety of text and symbols. The main feature of PictoChat is the ability to create simple drawings and post them onto the chatboard.
 Appearance in Super Smash Bros. Brawl
PictoChat appears as a stage in the game Super Smash Bros. Brawl. It starts off as a simplistic, flat stage, but as time passes, small sketches form on the stage. They can act as additional platforms, obstacles, or hazards to the combatants. The main platform will commonly say "Now entering:", with a random character participating in the match at the end. PictoChat is comparable in gameplay to the WarioWare, Inc. stage.
 Starting Songs in My Music
 Unlockable Songs in My Music