This pages lists glitches that can occur in Super Mario Bros.
Brick Block glitch
For this glitch to occur, a Brick Block must be partially hidden on the left side of the screen. If the character destroys the block while in Super or Fire form, the debris will not be rendered properly.
Bullet Bill glitch
This glitch occurs in World 6-3. The player must first find a mushroom platform to wait on. After a while (whether one is playing the NES or SNES version), one of the Bullet Bills, if jumped on, will fall on a string, similar to a Pulley Lift, but much slower. It will even occasionally remain suspended in the air. The player should note that, due to the long amount of time spent waiting for this glitch to occur, the level's timer will expire, costing the player a life.
Die and complete glitch
While playing through any castle level, the player should navigate through the entire area in the character's small form. As usual, the player must touch the axe to disable the bridge. However, if Bowser happens to touch the character at the same time the axe is touched, both the player and Bowser will die, but the player will still complete the level. If this is done with no lives remaining, the same thing happens, but the Game Over screen will appear after the player rescues the Mushroom Retainer.
Blue Bowser Glitch
In any Castle level, the player must go towards the end, but not on the bridge, at about the middle of the platform before the bridge. The player must stay where he is, and when Bowser appears, he will have an underground like color palette, much like his artwork.
in 6-3, find a Bullet Bill and if jumped on it will fall like a string. Much like A pulley lift but much slower.