The Halloween Hare can be found in three locations of Tibia on Halloween only (October 31st):
Mainland (around south of Dwarven Bridge near Venore and Kazordoon):
Dawnport (around northeast down 2 floors):
Rookgaard (around the Farm with Pigs and Sheep just west of the temple but will appear in the city normally when the farm has been left open):
Keep in mind he can be anywhere near these locations as he wanders a lot and doesn't seem to disappear when lured. I've seen him push some objects, but he cannot be pushed himself. Don't worry he doesn't hurt you, you cannot damage him as well. He tends to wander around a lot and will attack you (without damaging) from a distance and run away if you get close. In the past, I've seen him roped up the famous Mac Noodles near Venore. So have a look around, see if someone trapped him somewhere, and have a Happy Halloween!