Hammer Bros will only throw hammers at Mario and Luigi. They can throw a hammer at each Mario Bro. in one attack. Mario and Luigi can easily avoid these attacks by using their hammers to knock away the Hammer Bros. hammers.
Mario and Luigi Partners in TimeEdit
They appear as a boss, they are controlled by helmetes. They suked up Mario and Luigi and Baby Mario and Baby Luigi Fought them. After the helmets were destroyed in the fight, the hammer Bros. gave Baby Mario and Baby Luigi their hammers.