Bullet Bills; Enemies, Assist Trophies or fired by an item?

[cheat-master30]

http://www.dsultimate.net/Avatar/bulletbillbrawl.PNG

As you can see, Bullet Bills attack in Brawl. Does this mean they're assist trophies like the Hammer Bro is which is also an adventure mode obstacle, or maybe fired by an item you can pick up?

[elvis1835]

hmm i say an obsacle and only an obstacle like in adventure mode as that's what they have alway been in mario

[cheat-master30]

Maybe. So far though, the adventure mode looks far better than the one in Melee.