Grab your 3DS and get to downloadin’!
Right now, all you need to do to receive this Pokémon is connect to the internet with your 3DS, select Mystery Gift from the main menu on either Pokémon title, select “receive gift,” “yes,” and “get via Internet.” Select “yes” one more time and you’ll be gifted the special Pumpkaboo. You can then go and chat with any delivery girl at a Pokémon Center to receive your prize.
The Super-Size Pumpkaboo has a higher HP stat than smaller Pumpkaboos, and can learn the Ghost-type move Trick-or-Treat. You can enter the Trick-or-Treat Friendly Online Competition with this monster as well. To qualify, you need a Super-Size Gourgeist in your Battle Box as well, which you can acquire by trading your Pumpkaboo and watching it evolve.
What are you waiting for? Free Pokémon! Go get it!