These guidelines should be kept for any level that appears in the main SuperTux level sequence. Any deviation should be rare and with great consideration (for example for a secret area). Designers making custom levels intended for an Add-on or Bonus Island are free of regulations - that's what those sections are for. However, keep in mind that if your levels violate too many of these suggestions people will likely find them not very fun.
In Milestone 2, will have Icy Island as game discovering area, the island already present in Milestone 1. It has a snow and ice setting, so please use the appropriate tiles only. Most of them are in the “Snow” and “Blocks” groups in the level editor. There are numerous other tiles currently available in the editor, but they are either either not finalized (e.g. ice mountain) or not appropriate for Icy Island. In that first world, only basic elements should be found. It will present a revised Forest, where more elaborate elements may be found. The Boss have to be designed. And eventually a third world (proposed to be Tropical_Island) with the Fun Pif quest. Please Note that Neither art or code is ready yet for this part, then you shall not design any level with their elements already available.
The goal of SuperTux is to be fun, not to be hard. So the goal is to make fun levels, not to make them challenging. Remember that a player will get frustrated and annoyed if he dies more than small number of times in a level and also keep in mind that a player will see the level for the first time when he plays it.
Tip: If you are in doubt if a level is getting too hard, change the style of play to something that is unfamiliar to you, invert left/right controls, play with the left hand, play only as small Tux or anything like that. If you can still beat the level without problems and without dying, it likely is easy enough. If not, then it is likely too hard.
Do not randomly mix enemies of all different kinds. Level should follow a certain theme and thus focus on enemies that fit that theme. For example, fire enemies should only appear in castle levels. In addition, don't just randomly place each and every type of snow enemy into a level- pick a few enemies that best fit into your level.
Be mindful of how enemies react to the environment when deciding where to put them. For example, snowball will always fall off ledges while smartball will always turn around at a ledge, thus snowball is a poor choice in a sky level where smarball is much more appropriate. Enemies should not fall off the screen before players have a chance to engage them, and it should be possible to fill out the badguys killed stat. Finally avoid placing enemies where they will reach a spawn point. This is most important around the level start and reset points, as there should be ample time for a player to see and assess the level before being forced to act. Levels that switch back-and-forth between sectors are also prone to having an enemy wander into a spawn point resulting in Tux being hurt immediately after spawning- this is bad and makes players sad.
When creating slopes, make sure that they are smooth and don't make sudden jumps in inclination. Note when using slopes that some combinations are ill-fitting; ignore these artifacts as they are graphics problems, not level problems. You may want to avoid the use of steep slopes for the time being, at least until the slope collision physics are improved some more. Along those same lines, the placement of slopes directly next to a vertical wall currently produces some bizarre behavior and should be avoided until the mechanics are improved.
Don't use tiles in the background that were built for the foreground. Use only special background tiles in the background. In general, don't ever mix tilesets. Clearly distinguish between the layers - players should be able to see immediately where they can safely walk and what is foreground and background. Secret areas can violate this.
Levels must be at least 25 tiles high, and using at least 32 tiles is recommended. Levels should be between 250 and 350 tiles long. (A couple of levels in Icy Island are over 500 tiles long – newer levels should not be this long and it's possible we'll split up those long levels in the future.) Any vertical scrolling sector should be no narrower than 40 tiles wide to ensure it displays well in every resolution setting currently supported by SuperTux.
When saving the level file, stick with the convention used for the worldmap. For example, Icy Island levels are named like this: 02 - example level.stl where the number (02 in the example) showing what order you play the levels, and the level name are separated by a hyphen. The level extension is .stl, if you forget the extension, the level will not be recognized. If you need an example of naming convention, look at the data/levels/world1 directory. If level order does not matter, or is unknown, the number and hyphen can be omitted.
Note: having spaces in the level names makes command-line manipulation of files for development atrocious, there should probably be a discussion about changing the convention to use underscores in the level names instead.
However, it's not critical that custom levels necessarily follow the same naming convention. It is nevertheless best to stick with a non-cryptic naming scheme where it is obvious which file is for which level.
When making a level, use floors and ceilings where appropriate. Basic rule of thumb is that your environment should visually make sense. For example:
Transitions between sectors should also make sense. Having Tux walk off a screen of overground ice and suddenly appearing in the middle of a castle is confusing. Also one-way sector transitions should only be used where it is logical, such as dropping down a hole. Doors should be two-way. Sectors designed to be next to each other should be able to be visually connected.
SuperTux is meant to be a fair and fun game, so don't create unfair configurations, like a spike on the roof as well as one on the ground, that require way too much precision or luck and just aren't fun to play.
Other things to avoid:
These guidelines should be kept for any level that appears on the official world maps. Designers contributing levels to the Contrib and Bonus sections are free of regulations - that's what those sections are for. However, to maintain a certain level of playability, official levels should be designed with these rules in mind:
Don't mix tilesets! There shouldn't be any ice or castle tiles in a forest level, unless there is an obvious reason (like transition into another area).
Clearly distinguish between the layers - players should be able to see immediately where they can safely walk and what is foreground and background. Avoid placing bonus items (coins, boxes) in the background.
Be careful not to create dead ends. Test your level thoroughly to find possible paths you might have missed before.
Use everything the engine offers - but don't place it all in a single level!
Avoid large amounts of objects and badguys on the screen at once as it greatly decreases playability. Also, your level might not be playable on slower machines anymore.
Find the right difficulty! Too easy levels get boring very quickly while too hard ones can be frustrating. Levels you built often appear a lot easier for yourself, so be sure to let other people test them.
Don't make your level too short or too long - good size largely depends on the level's overall design, so there's no general "good" value. In longer levels, make sure there are enough reset points, so players won't have to repeat large portions of the level.
Secret areas should be well-hidden and not be visible on first sight. Use your imagination to think of new ways to create secrets - some of the above rules can be broken for that purpose, but be careful!
Icecrushers (Krush and Krosh) should be able to reach their original position and shouldn't get stuck anywhere in the middle when rising.