The Halloween Event
There are only two events that happen during Tibia's Halloween and they've been consistent for some time now, so I will let you know how it works.
The Mutated Pumpkin
The Mutated Pumpkin is an event boss that spawns every 4 hours starting right after October 31st server save to November 3rd server save. When he spawns it will say, "Oh noes! It's a mutated pumpkin!" To the left, I marked the three locations he spawns at. These locations are all close by in West Darashia. Your best bet to not miss him is to ask in English Chat when he will spawn, or count every 4 hours starting from the server save and arrive a couple of minutes early. I like to try to be 10 minutes early to be on the safe side. I stand in the middle of those 3 spots until he spawns. He can attack you, so just be prepared but he doesn't hit too hard. Also, he dies really quickly, it takes my server 30 seconds or somewhere around there before he is dead. I've also seen him lured to the city of Darashia in non-busy hours. I do recommend going to this boss at least once.
He is apart of the reward system so you need to make sure you do enough damage to him, use any high damage spells you can. I like to use SDs because I'm a mage. You actually have a chance of getting additional rewards if you didn't get any good loot from him you can also go to the portal that's east of Darashia and make sure you bring an Obsidian Knife and skin his body. You will also get the achievement, Mutated Presents which is 1 point only if you skinned his body. On the right is the location where you can skin him which is open only for 30 minutes. I'm going to list his rewards taken from my source:
The possible rewards from when he dies: Yummy Gummy Worms 10x, Toy Spider, Pumpkin 5x, Skeleton Decoration, Spiderwebs, Bat Decoration
One of the rewards from skinning him: Spiderwebs, Toy Spider, Bat Decoration, Skeleton Decoration,
Yummy Gummy Worms 20x, Red Surprise Bag, Blue Surprise Bag, Bar of Chocolate (Unsure of amount), Pumpkinhead, Pumpkin, Candy Canes 50x, Candies 50x
The Halloween Hare
The Halloween Hare can be found in three locations of Tibia on Halloween only (October 31st). He is considered an event creature. He is just for Halloween flavor and doesn't do any harm or drop any loot. He can turn you into any of these creatures for a total of 100 minutes or 1 hour and 40 minutes (whether you log in and out the timer is only counted when you're logged in, I personally tested this out)-
I'm going to show you where you can find him. 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.
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):