Although technically you can only get to 1000 (or 1100 total) lives in Super Mario 3D Land (after which your counter is replaced by a crown icon), this glitch allows you to get as many 1-Ups as you will ever need whilst playing through the game. It is debatable if this is a feature or a true glitch as with many previous Mario games, many feature areas to exploit the Koopa shell to gain near infinite lives. Find the straight moving Koopas found near the end of Stage 1-2 and and by jumping on top of one of them at the right spot, you are able to continuously bounce on top of the shell as it hits the wall and bounces back under you. This is easiest to do with the middle Koopa as shown in the video.
by ArcticExtras (Video)
Off-screen Bowser Button Freeze
Unconfirmed: At any ending stages where you need to press a button to remove the bridge from under Bowser to proceed, it is possible to “freeze” the game if by chance Bowser is off-screen. The game will not know what to do and Mario will be stuck in place. You will still be able to exit the level using the start screen; however, there is no way of proceeding normally after this happens.
As explained by TheMario901: This was done in World 1′s castle. I had the Tanooki suit so I decided to just float over to Bowser instead of taking the long way around. Bowser is at the very edge of the bridge right at the button when he starts shooting fireballs at you so I floated down next to him and he jumped backwards. I did a rolling long jump onto the button and I expected Bowser to jump back toward the edge like he usually does, but he didn’t. The bridge broke with him about halfway down it. I’ve done it multiple times but It hasn’t worked for me every single time I’ve done it.
by TheMario901 (Source)
Bowser Box Glitch
Ground Pounding a Bowser Box when you have the White Tanooki suit will cause the game to lock up and slow down for a couple seconds as the game constantly replays the stomping sound effect and particle effects from hitting the box. This same glitch does not happen when using the Star power – it will destroy as per normal, it is only effected by the White Tanooki suit.
by FrankyboyLegend (Video)
Stage S4-1 Enemy Trigger Glitch
Standing on the edge of the moving platform on Stage S4-1 will cause the enemy spawn trigger not to fire properly and throughout the level, most enemies will either not spawn at all, or spawn late in a way that drops them straight into the darkness.
by SuprMikey64 (Video)
Small Big Glitch
Similar to a glitch featured in the very first Super Mario Bros. game, you are able to both simultaneously grow bigger and shrink down from taking damage and getting a power-up at the same time. You should see both animations fire at the same time; however, you will stay small (but with the hat still on!).
Fall Death Item Switch
Missing Information: According to the video below, if you have one power-up activated, and another power-up in your item slot, switch out items, and then die in a level from a fall, when you re-spawn, and immediately “Go To Course Selection”, after which your item slot will change to the item you died with rather than the item you currently have.
It’s not clear in the video if this has to be the Fire Flower and Tanooki Leaf combination for this to work. It also isn’t clear if this will only work on Special 7-3 or not.
by manysonic17 (Video)