Masks are the part of a tileset that determine whether a particle is solid or is just eye candy. A good mask shows wat solids are in black. The unmasked portions of a tileset appear in purple in JCS.

Qualities that determine the usefulness of a tileset include the completeness of any given object or platform's solidarity, accuracy in terms of correspondence to visualized things in the tile and the ability of jackrabbits to negotiate the playing fields intended by the tileset. For example, a ramp should allow smooth direct access in comparison to stairs. Entryways should be large enough for any jackrabbit to pass through.

Tilesets can have different purposes in mind. For example, test levels use tilesets with clearly colored bricks. Hotel levels often use sets specific to the hotel's function. Regardless, certain shapes of blocks can be applicable to a wide variety of sets. For example, star blocks, question mark blocks, exclamation point blocks and figurehead blocks each imply or give hints to the user. Signposts allow for a direct message from the level's author. Masks for some of these common tiles can be identical.

In a Jazz 2 remake, we could use 7 types of mask:

1) Black: The solid block, that you stand on and stop at.
2) Jazz Transparent: The empty block, you walk through and fall down according to gravity.
3) Intense Purple: Triple gravity, making you jump lower and fall faster.
4) Lilac: Halved gravity, making you jump higher and fall slower.
5) White: No gravity. You can thrust yourself in every direction you want.
6) Brown: Ooze or swamp. You get stuck in it and move slowly, like in SuperMarioLand2's Tree Zone level 2, where you swim in the sap.
7) Blue: Water that you can swim into, like the Water Level event, but limited to the mask.

Most of those alternate mask types you suggest would work better as events than mask types I think... or as AngelScript features.

AngelScript? Yes, it would be awesome to have Jazz swimming on some tiles but without the water texture/refraction showing up. I think they should work on it.