http://www.supermariobrothers.org/smbxit's time to make levels
These rules are mostly cribbed from the Talking Time wiki:
* Each person can make one level per world. Try to fill worlds that have less levels.
* When saving level and graphics files, always put your name first, followed by the world it's supposed to go in, and then the level name itself. For example, "zaidyer-w4-rawhorsepower.lvl".
* You're allowed to use custom graphics and music. Always bundle them in a folder with the exact name as your level file. (Don't actually put the level file in this folder, SMBX episodes don't work that way!)
* Levels should be winnable with either Mario or Luigi. The only exception to this rule is if you've designed a level that absolutely needs a specific brother, because they have slightly different physics.
* Always put starting locations for both players. (In case of AWESOME, that's why.)
* Levels should always have a working checkpoint, no matter how hard you think the level is. The only exception to this rule is if you're building a level for World Nine. (Checkpoints may also be removed from levels in other worlds, but only if playtesting reveals they're not needed.)
* The game can only support one checkpoint per level. If you have multiple checkpoints, the first one the player hits will be the only one that counts.
* Levels should be winnable without being forced to take a hit.
* Never trap the player. If a certain item or powerup is needed to progress in the level, make sure it either respawns, or the player can die if he lost it.
* Enemies should always work the way they did in the game they're originally from.
* All water and waterfalls should be swimmable.
* Invisible blocks should never be made necessary to finish the level.
* Never put Lakitu in any area where you can scroll the screen vertically. He'll try to compensate by approaching infinite speed.
* The SMB3 Lakitu enemy is ruthless and can only throw those green rolling spinies. Instead of using him, pick the NPC you want and make sure the "Lakitu" option on the left side of the NPC panel is set to "yes". This will create a much tamer SMW Lakitu who will throw that NPC regularly.
* Horizontal autoscrolling is a bit glitchy. Only use it for flying levels.
* No Red Coin levels. But you can still use Red Coins if you treat them the way they worked in NSMB Wii: Hit a switch, and try to grab eight in rapid succession for a reward, before time runs out and they go away. You'll have to fiddle with events to get it to work, though.
* If you add Dragon Coins (Yoshi Coins), keep it to five on average, but no more than eight.
* Remember that if you put a powerup in a block, it will be a mushroom if Mario is small. Putting just mushrooms will mean they'll always be mushrooms no matter what. (Hammer and Tanooki suits will always be suits, as well.)
* Style your "end zone" with the Power Star like SMB3. Be sure to give a whole screen of black space and put the star where the old roulette would usually go. (It'll feel weird if you don't.) The only exception is for Secret Stars (to differentiate them) and any level where the Secret Star is hidden beyond the normal Star. (Like in Chocolate Island 3 or Cheese Bridge from SMW.)
* If you have horizontal warp pipes, don't put the warp on center or it'll look weird when you enter. Always put the warp on the floor. Also, make sure any such pipes have a floor or block in front of them you can stand on, even if they're underwater.
The theme of each world is:
1. Standard World #001: SMB1 assets only
2. Acqualand: Water
3. Cavey, Cavey Cave: Cave
4. Forest of Adventure: Forest
5. Obligatory Ice Level: Ice/Snow
6. Mt. Grep: Mountain/Sky
7. Brontocorp Inc. & Co: Structures/Metal
8. Hellfire By Night: Nighttime/Lava
Bowser's Castle (each player may submit a small castle area)
9. Secret (anything goes)