Java Edition 12w39b

12w39b was released to fix some of the bugs and crashes in the 12w39a snapshot.

Additions

 * Custom potions
 * Only available by editing in with a world editor
 * Able to create potions with multiple effects
 * Added command block arguments
 * Added "l" and "lm" arguments for indicating players with a maximum level, and minimum level, respectively
 * Added "r" and "lr" arguments for indicating the maximum and minimum range to which players will be affected
 * Added a command variable to the "/xp" command
 * Use "L" after number to represent number of levels, not number of xp.
 * For example "/xp 4L" will give a player 4 levels.
 * Added more options to customize spawners
 * Spawners can now have their range and maximum spawn limit customized.

Fixes
7 bugs fixed


 * “Lots of block placement issues with lighting have been fixed, but nether is still sketchy.”
 * Performance seems to be much better now
 * Fixed Bottomless Pit.
 * Pumpkin emitting stronger light from the wrong face fixed
 * Fixed the witch's texture being weird.
 * Partially fixed Nether lag by making the server do some of what used to be the client's work and increasing chunk load time slightly
 * Fixed some lighting bugs related to upside down slabs and stairs and farmland.