I love this! It looks like a lot of fun to play and a great adaptation of an iconic Mario baddie.

A couple of comments, just to clarify some things that seem a bit confusing or awkward. Mostly personal preference things.

Quote Originally Posted by Temotei
Bonus Feats: The hammer bro gains bonus feats chosen from the fighter bonus feat list in addition to Leap Attack at 1st and 3rd level. If Leap Attack is chosen, the hammer bro can use it whenever he charges, jumps, and is within a range increment of an opponent, rather than threatening an opponent. In addition, it allows Power Throw to be applied to it rather than Power Attack. Power Attack is not a prerequisite for Power Throw if Power Throw is taken as a bonus feat from this list.
The wording of this is a bit awkward, imo. I'd recommend something like, "The hammer bro gains bonus feats chosen from the fighter bonus feat list. He considers Leap Attack a fighter feat for this purpose. If a hammer bro chooses Leap Attack, he gains the benefits of the feat as long as he is wielding a hammer, makes a successful Jump check, and is within one range increment of his target. A hammer brother can apply the Power Throw feat to his Leap Attack instead of the Power Attack feat, if he so chooses. Finally, a hammer bro can select Power Throw as a bonus feat even if he does not meet the Power Attack prerequisite."

Or something like that. Just a suggestion that would make the paragraph read more smoothly in my mind. Take it or leave it.

Quote Originally Posted by Temotei
Hop (Ex): A hammer bro can hop once per round while moving. The hammer bro gains a +2 bonus to AC and thrown hammers gain a +2 bonus to attack and damage after hopping.
What exactly are the parameters of this hop? Does the hammer bro move? Does he have to make a Jump check? My guess is "no" on both counts, but the word hop implies some sort of movement so I figured I'd ask for clarity's sake.

Quote Originally Posted by Temotei
Collaborative Throw: At 2nd level, the hammer bro can attack an opponent within 60 feet that an ally hits as an attack of opportunity.
Another re-wording suggestion: "At 2nd level, when an ally hits an opponent with a melee or ranged attack, a hammer bro can also make a thrown hammer attack against that opponent as an immediate action." Also make sure to designate whether this is Ex or Su.

Quote Originally Posted by Temotei
Multi-Throw (Ex): Whenever the hammer bro throws a hammer, he can quickly throw a number of additional hammers equal to his hammer bro level. Successive hammer throws against the same target deal half damage.
What's the attack bonus for the follow-up hammers? How does this interact with full attacks? Can a hammer bro with multiple attacks per round use this ability on each one?

Quote Originally Posted by Temotei
Endless Hammers: At 3rd level, the hammer bro possesses an arbitrarily high number of hammers. The hammer bro never runs out of hammers to throw, pulling new hammers seemingly out of nowhere. Any hammers the hammer bro did not previously own do not have value, and so cannot be sold for currency. If the hammer bro enhances one of his hammers, all of them are considered enhanced, though they are still worth no money.
Again, what's the designation for this ability? Su? Ex? Something else. Also, if the hammer bro has multiple enchanted hammers, which enchantments apply to this ability. And why not call it "Hammerspace?"

Quote Originally Posted by Temotei
Hammer Maneuver: A hammer bro is so skilled with the thrown hammer that he may attempt to bull rush, disarm, sunder, or trip at a +2 bonus when throwing a hammer as if he was in melee combat and attempted the same. None of these maneuvers provokes an attack of opportunity.
I like this ability. Thrown hammers seem uniquely suited to ranged sunders and bull rushes, especially. Make sure you specify the hammer bro's size for some of these maneuvers, though. Bull rush and trip have size-based bonuses/penalties. Do thrown hammers count as one-handed weapons for disarm purposes?

Great, fun class! Thanks for posting it.