From the Super Mario Wiki
Hammers are items commonly used as weapons throughout the Mario series. It was the first item Mario ever used. They first appear in Donkey Kong, in which they are used to smash Barrels and enemies. Hammers are usually thrown by the Hammer Bros. and other enemies. However, Mario and Luigi have been known to effectively wield Hammers in combat. In the Paper Mario and Mario & Luigi games, Hammer attacks are used as a counterpart to Jump attacks. Some enemies cannot be damaged by Jump attacks (usually due to having a spiky top), requiring the Mario Bros. to use their Hammers instead.
In Donkey Kong, the original arcade game, Mario can destroy the barrels thrown by Donkey Kong, Fires created from the flaming Oil Drums, and Sand Piles in 50m. Mario is not invincible when using it, however. If attacked from the back, he will still lose a life. Mario also cannot climb or jump while wielding the Hammer. Hammers in this game can be found usually in the corners and some can only be reached by jumping.
In Donkey Kong for the Game Boy, Hammers make a reappearance. They can be used to defeat all enemies in the game. Super Hammers can even break brick walls. In this game, Mario can throw Hammers upwards. At several points in the game, the player has to throw the Hammer upwards, then quickly climb the ladder onto the next platform above to pick it up again. If the Hammer touches a floor, it disappears instantly.
Super Mario series
Hammers are used in Super Mario Bros. 3 as a map screen item to destroy boulders preventing access to hidden areas. Usually, a Hammer just allows Mario to produce a quicker route, but in some cases, it is the only way to access a part of a map. In Desert Land there is a section in the upper right corner that leads to an area that contains a Toad House with a Frog Suit, and a Fire Bro battle containing the last Warp Whistle. In Water Land, there is a section leading to a canoe ride which takes Mario or Luigi to several Toad Houses and Spade Panels.
Mario repeatedly used a Hammer in the German Club Nintendo comics. In 1994 "Super Mario: Verloren in der Zeit", he smashes his alarm clock (due to his dream in which there was an alarm clock-looking Time Machine). Later, in the 1995 comic "Mario's Picross", Mario makes a more effective use of a Hammer when he smashes the wall in a Pyramid, after reaching a dead end. While in the first comic the tool looks a lot like a regular Hammer, it resembles a Super Hammer in the latter.
Mario & Wario
During the bonus mini-games after most stage areas, Wanda the fairy will hold a hammer rather than her usual wand and be able to whack Wario's plane for coins. She can collect forty coins before he flees.
Super Mario RPG: Legend of the Seven Stars
In Super Mario RPG: Legend of the Seven Stars, Mario's first and weakest weapon is called the Hammer. After Mario beat the Hammer Bros. blocking the exit of Mushroom Way, Mario receives a Hammer apparently dropped by them with the Hammer Bros. insignia on it. The plumber uses this weapon to pound enemies, at least until he finds the Nok Nok Shell. When equipped, the weapon adds ten attack points to Mario's attack rating. When Mario uses it with the Timed Hit, he swings it up and down twice, similar to the old style. Later on in the game, he finds more advanced Hammers: the Super Hammer, Masher and the Ultra Hammer, along with another Hammer with an added effect.
Paper Mario series
In Paper Mario it is given by Goompa after finding him and his Hammer lost in the bushes. Jr. Troopa is the first one lucky enough to be tested on. Spy Guys also have Hammers, and these hammer attacks can cause Mario to lose one of his Action commands for about five or four turns. In Paper Mario: The Thousand-Year Door it is a default weapon and it is degraded again into a normal Hammer. The first Hammers in this series are wooden.
In these two games, Mario receives not only the Hammer, but the Super Hammer and Ultra Hammer as he progresses through the adventure. In Paper Mario, the Super Hammer is found in Dry Dry Ruins, and the Ultra Hammer is found in Mt. Lavalava. In Paper Mario: The Thousand-Year Door, the Super Hammer is given by Podler in Glitzville, who in turn received it from Jolene, and the Ultra Hammer is found in Rogueport, but Mario must use Spring Jump to get it.
In battle, Jump attacks can not work on every single enemy, so the Hammer is introduced as an alternative. It works on all enemies and is always stacked damage, proving useful against fire, spiked, and high defense enemies. There is one flaw to it though; it does not work against air-bound and ceiling attached enemies. With a special badge, namely Hammer Throw, it can be used on all enemies.
Outside of battle, the Hammer can be used to knock items out of trees, break certain Blocks. The type of block Mario can break depended on what type of Hammer he had. In Paper Mario, Yellow Blocks can be broken by any Hammer, Stone Blocks by the Super Hammer and Ultra Hammer, and Metal Blocks by only the Ultra Hammer. In Paper Mario: The Thousand Year Door, small yellow blocks can be broken by any Hammer, big yellow blocks by the Super Hammer and Ultra Hammer, and stone blocks (big and small) by only the Ultra Hammer. Metal blocks can't be broken by any Hammer. The move, Spin Hammer is introduced in Paper Mario: The Thousand-Year Door as the way to destroy big blocks.
In Paper Mario: Sticker Star, multiple Hammer stickers can be found throughout the game. While Mario can still use his hammer within the overworld, there are a variety of Hammer stickers found in the game, including:
Every Hammer in the game has a Worn-out (Hammer Only), Shiny (not Baahammer, Burnhammer or Chillhammer), Flashy (not Baahammer, Burnhammer or Chillhammer), Big Shiny and Megaflash variants.
Concerning the overworld hammer, Mario obtains this at the beginning of the game, after recovering from Bowser's attack on Decalburg. In World 3-7, Rustle Burrow, Mario loses his overworld hammer; as such, he is unable to use Hammer stickers in battle.
Mario & Luigi series
The Hammer is used by the Mario Bros. in Mario & Luigi: Superstar Saga, Mario & Luigi: Partners in Time, Mario & Luigi: Bowser's Inside Story, and Mario & Luigi: Dream Team. However, this move is not used as much compared to the Paper Mario series. Unlike the Paper Mario series battle system, each Hammer upgrade do not affect in-battle damage and attack power.
Mario & Luigi: Superstar Saga
In Mario & Luigi: Superstar Saga, Hammers are crafted by the Hammerhead Bros. out of Hoohoo Blocks. They are used to smash rocks (instead of blocks) in Mario and Luigi's path, defeat enemies in battle, and hit special buttons and switches. If used on an enemy in the overworld, its party will be stunned at beginning of the battle. They can later be upgraded to Super Hammer and, ultimately, Ultra Hammer, like the Paper Mario series. After Cork and Cask teach them the advanced method of using the Hammer they can use various overworld and battle abilities.
To do more damage in battle, Mario or Luigi must press their button when the hammer shakes.
Mario & Luigi: Partners in Time
In Mario & Luigi: Partners in Time, two Hammers are given to Baby Mario and Baby Luigi by the Hammer Bros. These weapons can be used to tunnel underground to dig under walls and fences, dig up Beans, and hit switches. In battle, Baby Mario and Baby Luigi can use their Hammers to attack enemies. The hammer can be used overworld to potentially stun enemies for a first strike. Unlike the other Mario RPGs, these Hammers serve their purpose for the entire game and are never upgraded.
The action command for the hammer is the same: the player should press the button when the hammer shakes. If the babies are carried by the Mario Bros. during battle, the player must press a Mario bro's button to lift up the baby, then press his baby button.
Mario & Luigi: Bowser's Inside Story
In Mario & Luigi: Bowser's Inside Story, Mario and Luigi gain Hammers much earlier than in the other Mario and Luigi games. Mario and Luigi find Hammers in the Trash Pit. Later, Luigi learns how to turn Mario into Mini-Mario by using his Hammer in Pump Works to free Toadsworth.
Hammers in battle are used quite differently. Mario or Luigi must press their button at the very last moment before the hammerhead falls. Doing so gives the player an "Excellent".
Mario & Luigi: Dream Team
In Mario & Luigi: Dream Team, a Brock in Mushrise Park lost his hammers that he was supposed to use smash rocks with for his boss, Brickle and ordered new ones. So, when Mario and Luigi found the lost hammers, he let the Bros. keep them. Also, after this point in the game, you can go to shops and buy hammers like the Run-down Hammer and the So-So Hammer.
In battle in the Real World, the hammer attack stays relative to how it was in Mario & Luigi: Bowser's Inside Story. In the Dream World, the hammer attack is amplified in power as after Mario hammers the ground with his hammer, a group of Luiginoids appear and smash the ground in unison with their own hammers, sending out a wave that damages the enemies at the front the most, and the ones at the back the least. During Giant Battles, the hammer is split into two forms of attack, those being the Hammer Chop and Hammer Uppercut techniques, each requiring a slightly different action command to execute successfully.
Earthwake, the third giant boss turns into a hammer sometimes and swings itself several times. Pi'illodium, a late-game boss also takes the shape of a hammer and counts down from a mere 4 to a generous 6 as an attack to smash Mario and Luigi. The final boss of the game, Dreamy Bowser uses a giant Hammer as one of his many attacks to try and crush Mario and Luigi. Unlike the other games, Mario and Luigi can hold their hammers indefinitely when counter-attacking.
Mario vs. Donkey Kong series
Super Smash Bros. series
The Hammer from Donkey Kong is a powerful item in the Super Smash Bros. series. The player will swing the Hammer back and forth repeatedly, and will strike anything upward in its path. The character cannot double jump with it. Very rarely, in Super Smash Bros. Melee and Super Smash Bros. Brawl, the head of the Hammer will fall off, and the character will swing the Hammer's handle back and forth, leaving them completely vulnerable. However, the head will act as an item, and will have the same power as the regular thrown item. When the Hammer is used, the Hammer theme from the original Donkey Kong arcade game plays. The item returns in Super Smash Bros. Brawl, with the exact same effects. A much stronger variant originating from Wrecking Crew, the Golden Hammer, appears as an item in Super Smash Bros. Brawl as well. Kirby and King Dedede use a hammer attack in the game.
Mario Party series
In Mario Party 3, Toad uses a hammer as his weapon when he is a partner.
Hammers are also used in other minigames in Mario Party 1-3.
Hammers reappear in Mario Party 9 in the minigame, Spike Strike, where players have to defeat the giant Spike using hammers. There is also one golden hammer for each round. If a character uses it, that character will earn three points, while iron ones are worth one.
DK: Jungle Climber
The Hammer in DK: Jungle Climber looks somewhat like a Barrel. Donkey Kong can take it and, with the help of Diddy Kong, use the Hammer to smash barrels, rocks and other solid elements that Donkey Kong cannot break in his own. This item can only be used for a limited time before Diddy Kong drops it.
Mario Tennis series
Super Smash Bros. Melee
Super Smash Bros. Brawl
Super Smash Bros. for Nintendo 3DS / Wii U
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