Most of these are either common sense tips or just little tricks I've figured out over time. These tips should help no matter what level you're editing, and some of them apply to things other than Sonic 2.
- If you don't know what it is, it's best not to ignore it, as it'll probably bite you in the ass later. Especially tags are dangerous little objects to ignore. Also, test frequently. I can't stress enough how important it is to test frequently and make a backup after every successful test. You WILL screw up, it's only a matter of time, and you don't want to lose anything important when you screw yourself. I personally have gotten a file named "Copy (42) of sonic2z.bin".
- Bottomless pits will only kill Sonic and Tails when the tile at the top of the map is clear at the top. Having a tile that blocks off everything at the top of the map will cause the pit at the bottom not to kill the player. Make a note of this if you're going to use bottomless pits.
- Tiles won't always go the way you want them to, but sometimes there is something you can do about that. The object 74 is an invisible wall of varying size, depending on the second value. The trick is, if a tile isn't working for you, and you don't have an alternative, you can insert an invisible wall to change what the tile will do. I use this trick a few times in ARZ to avoid driving myself insane.
- Figure out what the numbers of the general tiles that you're gonna use a lot are, and memorize them. Flat spaces and solid walls are something that are going to be used quite a bit, and it saves a lot of time to memorize what they are. Don't forget the G key in SonED so you can grab tiles.
- Because of the nature of Sonic 2, having too many objects onscreen at once will cause slowdown and sometimes even visual glitches. Make SURE that any objects you have near each other don't contradict each other. Also, when the boss appears, many other objects will also glitch. Generally, anything but the very basics will act weird when the boss appears, so don't think about doing something elaborate for the boss, because chances are it won't work.