The Pokemon Company has a special Halloween-themed online X & Y competition lined up for October 24 to 26. The Trick-or-Treat Friendly is a battle of Ghost-types only (Rotom and Giratina excluded), and you'll net five Rare Candies simply for entering. To qualify, your Battle Box needs to contain a Super Size Gourgeist, which evolves from a Super Size Pumpkaboo after being traded.
To help players along, a Super Size Pumpkaboo has been made available to all over Nintendo Network through the month of October. This special Pumpkaboo comes equipped with Trick-or-Treat and Scary Face, and it’s holding a Rocky Helmet item, which deals return damage to your attacker.
This is also a good time to remind everyone that Shiny Gengar can be downloaded from GameStop between October 13 and 26. You'll be able to use it in the Trick-or-Treat Friendly as well, as long as you remember to sign up between October 16 and 23. The full competition rules can be read here.