Normally, Mario can only use the Mega Mario for 1 minute, if the player uses this finisher when Mario become KO'd, Mario will appear in the Mega Mario form, but, with the same power of the normal Mario, if the player have only 1 HP, the player become immortal, the only way to defeat Mega Glitched Mario is using the Star.
In Dark Castle or Sky Plains, has been hitted by a enemy while in the cage and use the finisher, Luigi will be killed, but, the fight doesn't end, the game acts like Luigi is alive and the game goes forever, the only way to reverse this is reseting the game.
Luigi can do a second jump via a glitch. In Cloudy Caves, jump into a cloud and use the finisher while you are in the air, Luigi, strangely, will do a second jump
This glitch happen normaly in the game, if the player chosses the Koopa's Cave as arena, Peach will appear in a strange sprite, like she was sneezing.
It's rare, but, if the player pulls out a vegetable while playing as Toad, and press the button to release the vegetable on the time Toad lifts the vegetable, Toad will release the vegetable, but, he will appear like he is with the vegetable on hands.
If you use the Shake It ability on the enemy who is well, right next to you, you gonna KO'd the enemy, but, Wario will stay shaking nothing.
If you use the Waluigi's Arsenal ability and see very close to the screen, you gonna see, the Bom-Omb graphic is glitched.
Yoshi's Stampede occasionly can glitch out the game graphics. This has been fixed in Nintendo Wii Era DLC.
Bugs and Glitches (Secret Characters)
SMB2 Characters (Peach & Toad)
The same thing of Toad happen with SMB2 Characters (Peach & Toad).
SMB3 Characters (Mario & Luigi)
If you use the Tanooki Suit as SMB3 Mario or Luigi, sometimes, he gonna drop without a reason. This has been fixed in the Patch "Bug Fixes Season #2".
SMB Bowser & Bowser
SMB Bowser and Bowser needs charges the fire, but, sometimes the Fire doesn't appear. This has been fixed in the Patch "Bug Fixes Season #1".
NES Mini Mario
This is curious, if NES Mini Mario touches any power-up, the game will glitch out, this glitch can be done in three ways:
Play as any character and let the CPU chosses him, go a stage with a power-up block, hit him, and make the CPU gets next him.
Play as NES Mini Mario and let the CPU chosses any character, go a stage witha power-up block, hit him, jumps next to him, waits the CPU hits you and you need land on power-up.
This only can be done in the Story Mode in the last boss, make sure you have 2 lifes, have 5 HP or less, jump next to a power-up and waits the boss hit you and you need falls into the power-up and dies.