Transparent tiles...
 

Does JJ2 support them? And if yes... how can I draw 'em?

well you can draw them, but it's easier if you click right click on the tile what you want to be translucent (when you make the tileset), then type > translucent. Also it is possible if you press 'T' when your mouse is on tile in the tileset, and click on Translucent and ok.

Cool, thanks.

I won't talk about what JJ2 supports, because people (Violet) keep finding out that it does some pretty weird and unexpected things. JCS tileset compiler anyway, supports only 0% and 100% transparency. The only way to make something partially transparent is the "Translucent" type of tile (the transparency is about 40% then, to make it lower you can use other layers and you can't make it higher). Also, take a note that the Translucent tiles still use only the existing palette entries.

This is one of the things which keeps the tiles graphics impossible to make perfect and as a tileset maker you will have to deal with this. The others are: palette, tiles limit and layers limit.

Only way I know of making the tiles somewhat transparent is by making them... how should I say... kinda' like a chess table (1st color 100% transparent, 2nd color 0% transparent, or the opposite).

Speaking of palettes, happen to know how I can apply the palette to an image in Paint.NET?

True, but this never looks really well, especially in case of more detailed things (like sprites) behind it. Sucks even more when the transparent thing is supposed to have a shape itself. Even using that built-in "Translucent" option is a smarter thing to do.

As I'm not using the Paint.net, the only thing I can suggest is to download TilesetPal instead, since it's a tool made specifically for JJ2 tilesets and so it's the easiest in use color reduction program for them. Do whatever you want though.

Already have it :P IDK what exactly it does tho.

By the way can't seem to find that translucent option.

TilesetPal reduces an image from 24-bit to 8-bit. It does it pretty well, too.

And for the translucent option, hold your mouse over a tile in the tileset viewer and press the T button. Then you can set it to translucent. Keep in mind that it affects the tile wherever you use it in the level.

Warm and fuzzy as I feel reading that, don't expect any changes on that front. Tile transparency masks (whether a given pixel is opaque or not) are stored basically as bits, so there's no room for any in-between values, and transparent is one tile type out of potentially several but stored in a single byte (the only other working option being Caption), so that can't plausibly be stored as a scale.

Ok... what?

I recommend to not get used to pressing the T button, or it'll be pain if you'll be ever using Prismatic Palace or something else needing much Translucent tiles. Shift+T sets the tile to Translucent without unnecessary additional windows.

He said that JJ2 doesn't support partial transparency other than Translucent tile type.