They're like Pokeballs, except any Nintendo character could pop out.
Besides our roundups of the Smash Bros. Dojo updates every Friday, we promised our readers that we'd write specific news articles anytime the official Smash blog announced something really big, like a new feature or a previously unknown character.
Today, the Dojo ran two updates, both about Assist Trophies. These items seem to function the same as Pokeballs, but they contain characters from all sorts of Nintendo games. Basically, the collectible character trophies from Melee have been worked into Brawl's gameplay. This means that a far wider variety of Nintendo characters will make appearances during battle, although like the randomly generated Pokemon, the trophy helpers are invincible and controlled automatically.
The three Assist Trophies revealed today are Hammer Bro (throws hammers), the giant Nintendog first shown at E3 2006 (blocks most of the screen), and Samurai Goroh (runs around and swings a sword). The blog promises that some of the trophies will be quite obscure characters, although they may be less obscure after appearing in Brawl.