Most of the bosses that Mario and his team must fight for a Star Piece are weapon based:
• Mack rides a pogo stick in the shape of a large throwing knife.
• Bowyer is a large, anthropomorphic bow who fires anthropomorphic arrows.
• Punchinello is a large, anthropomorphic bomb who utilizes Bob-Ombs in combat.
• Johnathon Jones wields a trident, and Yaridovich is a large, anthropomorphic spear who also wields a spear.
• The Axem Rangers wield axes and comandeer the Blade, a ship in the shape of a battle axe's blade.
• Smithy wields a giant hammer.

Note that with the exception of Punchinello and Johnathan Jones, all of these bosses are members of the Smithy Gang, the group of antagonists of the game; these allusions to weapons reference Smithy's goal to fill the world with them.
Contributed by game4brains