Minecraft's Halloween update will bring a new portal system to the game, courtesy of a new dimension, tentatively-titled "Hell". Sounds cushy! Such convenience, however, comes at a price.
This new dimension will be guarded by a new monster type, called the Ghast. It's a floaty jellyfish thing that shoots fireballs, which explode when they hit something, then set what's left on fire. Even the ground.
You'll only encounter Ghasts while traversing the "Hell" dimension, so if you want to enjoy the luxury of fast-travelling across your Minecraft maps, you'd better be prepared to run.