Mega Mario

Mega Mario is a form that Mario and some others can become by eating a Mega Mushroom or simply Super Mushrooms in many games. This form allows the player to greatly increase in size, allowing them to defeat every enemy in his path and break almost anything (including Flagpoles).

Super Mario 64 DS
In Super Mario 64 DS, the Super Mushroom has the same effects as the Mega Mushroom, and makes the player into a larger size. The player can then obliterate almost anything in his or her path, and if they break more than eight objects, he or she will get a 1-up for every additional object they destroy. The Super Mushrooms are always found in Bricks scattered throughout the level and are introduced in Bob-omb Battlefield. The player cannot do any special types of jumps, such as the Triple Jump. If Yoshi grabs a Super Mushroom, he gains the ability to punch.

New Super Mario Bros.
The Mega Mario form returns in New Super Mario Bros., being obtained from the rare Mega Mushroom. The more objects Mega Mario breaks, the bar above his head will get filled in. If he crushes a certain amount of objects, Mega Mario can gain up to five 1-Up Mushrooms. Mega Mario also has the ability to squash any of New Super Mario Bros. ' bosses in one hit, including Bowser in any of his forms. If Mega Mario falls into a pit, the purple toxic water or lava, or if time runs out, he is instantly defeated. When the power-up expires, he is reverted to Super Mario, regardless of whatever form he was in before using the Mega Mushroom. If the Mega Mushroom is activated in tight spaces, Mario's transformation will be canceled and the Mega Mushroom will return to the touch screen. Additionally, if Mega Mario completes the level, he destroys the flagpole, shrugs, and automatically recieves 3 1-Up Mushrooms.

New Super Mario Bros. 2
The Mega Mario form returns in New Super Mario Bros. 2, again being obtained from the Mega Mushroom, acting the same as in the previous game. However, unlike New Super Mario Bros., Mega Mario does not gain 1-Up Mushrooms for destroying blocks.

Mario Party 3
In the mini-game Toadstool Titan of Mario Party 3, characters could grow giant by obtaining the Mushroom hidden in one of the several Brick Blocks every round. Once the character had obtained the mushroom, he or she was capable of knocking out other characters in a short period of time. Mega characters could not jump and control their moves, however, instead charging in whatever direction they are facing.

Mario Party 4
In Mario Party 4, the Mega Mushroom cause one to enlarge in size and hit two Dice Blocks. While Mega, the player can take 10 coins from any opponent the player squishes. The Super Mega Mushroom works the same way, but with three Dice Blocks.

Super Smash Bros. series
In Super Smash Bros. Melee and Super Smash Bros. Brawl, any character can become Mega by acquiring a Super Mushroom. When a player is Mega, his or her attack power increases by a fair bit and launch resistance increases. However, it makes the character easier to hit and pelt them with attacks. In Super Smash Bros. Brawl, the final event match pits the player against Mega Mario, Snake, and Sonic. Both games also offer an option to play as Mega for an entire match.

Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Mario or his partners can become huge by using a Power Punch. This increases their attack power briefly for a few turns. During a few Bowser intermissions, if he eats enough Meat, it has the same effect as a Mega Mushroom and makes him huge, invincible, and destructive for a brief time. Princess Peach can also swallow a potion that makes her momentarily giant, although no other effects are seen.

Super Paper Mario
In Super Paper Mario, when Mario (or Luigi, Princess Peach, or Bowser) grabs a Mega Star, they will turn 8-bit, much like their sprite from Super Mario Bros. and grow to giant proportions as well. As Mega Mario, Mario will be able to break blocks, enemies and anything in his path, much like the Mega Mario form from New Super Mario Bros.. Mega Mario and Luigi are shorter and faster, while Peach and Bowser are taller but slower. In Chapter 3-1, there is a specific Koopa Troopa that collects a Mega Star, causing it to become massive; it is known as the Mega Koopa. According to the InterNed, the music plays while one of the characters is in Mega form (including the Mega Koopa) is titled "An Unrivaled Battle".

Additionally, by feeding Princess Peach a Red Apple while she is in her comatose state, she momentarily grows to a giant size.

Mario Super Sluggers
In Mario Super Sluggers, any character can become temporarily Mega by finding a Mushroom in the mini-game, Graffiti Runner. When a player is giant, he or she can create small earthquakes that can paralyze all ground opponents for a brief period. However, they are still vulnerable to body checks, Chain Chomps, and characters that have a star in effect.

Mario Kart Wii
In Mario Kart Wii, Mega Mushrooms appear as items. When the character utilizes the Mega Mushroom, then he or she becomes gigantic, allowing him or her to squish opponents and get a speed boost. However, the player is not immune to Thunderbolts, invincible racers or Bullet Bills. When the player is hit by a Thunderbolt, they simply revert back to their original size.

Mario & Luigi: Bowser's Inside Story
In Mario & Luigi: Bowser's Inside Story, one of Broque Monsieur's attacks during his battle with Bowser involves hitting a block and obtaining a Mega Mushroom. While mega, he attempts to ram Bowser, but this attack can be countered by punching him.

Mario & Sonic at the Olympic Winter Games
The Mega Mushroom appears in the DS version of Mario & Sonic at the Olympic Winter Games, in the Dream Curling event. Some of the panels appearing on the ground are Mega Mushroom panels, which cause the stone to increase in size.

Trivia

 * A similar form to Mega Mario, though unnamed, appeared in the Club Nintendo comic "Mario in Mariozilla". Kamek accidentally turned him into this state.
 * In The Super Mario Bros. Super Show! episode, Mario Meets Koop-zilla, Mario becomes Mega Mario, but not by a Mega Mushroom, but by the Super Sushi. Interestingly, this was before Mega Mario appeared.