Hetalia: Halloween episode is a hard to find extra episode from the popular anime, Hetalia: The World Twinkle. It was released on DVD on February 24, 2016. But only in Japan. The full episode can not be found online. However a few screenshots and a short 15 seconds clip of the episode has resurfaced on the internet. On February 8th, 2016, there was a livestream of the episode that was shown only once on the internet. However, the full episode was on youtube, but was taken down shortly after. The livestream has not been mirrored anywhere else on the internet. Other then that, the episode can't be watched online. However, FUNmation will be releasing the OVA dubbed in DVD and Blu-Ray.
The full episode can be found with the original Japanese dub with spanish subs, in the Facebook page "HetaRandom" (https://m.facebook.com/hetalia.random.es.amor0296/videos/hetaween-2013/1090218217699225/). The post also features two download links, one with Mega (Doesn't work anymore) and one with MediaFire (Still works).
There is a full episode with Japanese Dub with English sub on https://vimeo.com/173801222
The episode can also be found on YouTube with the English dub, updated by the user Foyota 0127.