Basically there are two types of weapons for Halloween event:
 
Craftable – There are a number of weapons that can be crafted from materials that come from Halloween content. They are exotic and they have their own stats. You can craft these at any time of the year, but there are certain components that will only drop during Halloween. Since these weapons are really cool, we allow you to rent them from an in-game vendor in Lion’s Arch. They’re pretty cheap (you can buy them without paying gold) and yes, they expire in four hours. Basically, everyone will have a chance to get in the spirit of the season. To that effect, these weapons have auto-scaling stats but you can’t transmute them. For those of you who want to stay “festive” all year round, you’ll have to delve in the content and put the weapons together.
 
Purchasable Skins – These are available in the Black Lion Chests. They are a one-time use skin that you can apply to anything, I believe, and from there transmute that appearance to something else if you need to. You cannot rent these from that vendor in Lion’s Arch.
 
There’s also a bunch more gear, goodies, and crafting recipes to be discovered in the content itself!

The craftable skins and the Black Lion Chest skins are completely different from one another

You don’t necessarily need weaponsmith maxed, but the permanent craftable weapons are level 80. And they are sellable.