Those rules must be followed when designing levels:
(Most of them will have built-in protection in editor)


Level:

-A level must be at least 10 tiles high and at least 15 tiles wide

-Treasure box: Empty space, water or water surface in the next tile above

-Slope ground: Must have at least two tiles of free (non-solid) above

-A level must have a background

-A level must have at least one exit that can be reached (End, trigger, or treasure)

-When enemies that carry treasures is present there must be empty space just above the floor
 close to this enemy

-Hammerman must have at least 2 levels of tiles of solid ground below to avoid falling through the ground










Map:

-At least one level must be completed before it is possible to enter doomship

-A map must be at least 10 tiles high and at least 15 tiles wide

-A boat can not be placed in slot 0!


Levelset mapmode:

-A map mode levelset must have a levelfile not containing any world, but common stuff like mushrom house, 
 map monsters, moneyship, warp zone etc.