A hammer-throwing Koopa who stands on brick platforms and lobs hammers in arcs. One of the most dangerous standard enemies in the game — hammers travel in parabolic paths that cover both close and far range, and the Hammer Bro itself jumps unpredictably.
Hit it with fireballs from a safe distance — the easiest method. You can stomp it but timing is tricky as it jumps frequently. Running under it at close range when it jumps can work, but is very risky.