Universal Features:
-Thick, moody fog and orange sky
-Purple clouds
-Per-biome water coloring and transparency
-Accurate bed and shulker coloring
-Instant-transition block animations
-Improved block rotation
-Textured piston arms
-Solid crosshairs
-Pumpkin Minecoins (and other minor menu changes)
-Music player integration
-Java/Console Aspects compatibility
-4JD UI panorama support

Halloween 2015 (Mash-up Style) Exclusive Features:
-Cohesive grass textures
-Unique stained glass textures
-Unique wool textures
-Transparent birch, spruce, and dark oak door textures
-Natural sculk and Nether stem animations
-Accurate Mash-up world panorama
-Unused: Green-tinted lightmap textures

Halloween 2013 (Classic Style) Exclusive Features:
-Overhauled menus
-Monster-focused paintings
-Normal Minecraft music
-Spooky Nether panorama
-The following blocks are no longer animated:
  -Dandelion and poppy
  -Green and pink wools
  -Cactuses
  -Glowstone
  -Nether stems
  -Sculk and sculk vein