Both SNW (Oct 28-Nov 4) and sGE (Oct 29-Nov 19) are also having the event previously mentioned for twGE. For details, see Semana de los Muerte (SNW), Halloween Monster Race (sGE), and Halloween Event 2009 (twGE). I will just post some things not mentioned in the 3 articles linked above...
The Strolling Witch is located in Auch (D6, Channel 1 ONLY), offering standard rewards, bonus rewards, and server-record rewards. SNW has the same standard/bonus rewards as sGE (see Halloween Monster Race), but server-record rewards are probably different. The stats of the 2-day back costumes were mentioned previously here, and the ones for bonus rewards are permanent with no stats.
There seems to be 7 possible missions in all - 3 low-level (available to family level 1-15), 3 high-level, and 1 boss. The exact mission is randomly determined within its category (low-level, high-level). The following missions are taken from SNW, but it should be the same for sGE as well. (If it isn't, please leave a comment.)
- [Lo] Elite Striped Spider x60 (Al Quelt Moreza Nartex) + Elite Vedanobah x60 (Al Quelt Moreza Nartex)
- [Lo] Elite Phobitan Imp x110 (Tetra Hill, Tetra Ruins) + Elite Lazim x45 (Tetra Hill)
- [Lo] Elite Gavi di Gavi x60 (Porto Bello) + Elite Merman x30 (Porto Bello)
- [Hi] Grim Reaper x40 (Ferruccio Wall) + Plain Phobitan Imp x115 (Lago Celeste)
- [Hi] Swamp Spider-Crab x110 (Bahamar Wetlands) + Villain x75 (Topolo Durga)
- [Hi] Diseased Capybara x95 (Abertal) + Skeleton Raptor x150 (Ustiur Zona Cuatro, Skeleton Dungeon 3F)
- [Boss] Jormongand x1 (Vegas Javier) ... See Garim's Nest for details.
Use the Witch's Pocket Watch (you get 3 per mission) to get the time, so that you can complete the mission marginally before your previous record in order to get the bonus reward and make it easier for the next mission. Note that if you give up on the mission, it still counts towards your daily limits (3). Since it is about kill counts, you may squad with other players for faster kills.
Update: The Witch's Candy is a non-tradable buff item affecting all active characters for 1 hour (3,600 seconds), granting EXP +20%, Stance EXP +20%, and Movement Speed +10%.
Unfortunately, you cannot dump these event back costumes into the Costume Collection Chest. Thanks to SnowHusky and lolathe for providing more info on the low-level hunts.