Spectres are spirits of the deceased returned with a vengeance. Bound to physical objects they are reminiscent of an incorporeal lich.
This sounds as if it would be a creature far deadly then the lich could dream of being, but sadly due to their limitations it can never be true. Unlike the lich who are free thinking capable of amending goals and even completing them and moving on to find new goals, the spectre exists largely for one goal. Once this goal is achieved they tend to go into a rest period until such a point where it can be achieved again or an outside source forces them awake.
In addition, Spectres tend to have rules to their method. Such as can only kill victims when they scream, can only attack while they're sleeping, only people wearing purple, so on. the allows you to better fight them as any weakness learned can be exploited. As well, what they are bound to in the after life is directly based on their life. A spectre of a doll maker for example would be bound to one, some, or most of his dolls for example. The destruction of this link is enough to destroy the spectre permanently, unlike the lich who can rebuild from just their body.
These disadvantages however do not make them easy to deal with. as intelligent in death as they were in life and with a host of new ghostly abilities the spectre tends to set up long term plans for whatever their twisted goal is. sending parts of the things they are bound to for a wider area to spread their terror is a common trend, or is used as a lure if they are trying to kill specific people.
the are aware of their weaknesses, know what they are bound to, and can plan accordingly. often if multiple objects are involved one or more may be hidden as a fail-safe against discovery. possessing skills from life they can usually utilize them in their schemes. this becomes less useful for a spectre of a construction worker, but for an former actor or puppeteer it becomes invaluable, able to lead people to their untimely death.
A spectre's creation is never the same for any one of them. Typically it involves the person being connected to dark magic and being murdered in a traumatic manner. There are those who choose this fate on their death bed figuring revenge is better then a peaceful rest, and there are even some who had no intention of becoming such and happen into it. All said, the person the spectre was was largely evil to begin with, and death removed any good once held within them. The new creature while identifiable them, possessing all their memories, and for all intents and purposes are them, possess none of their good qualities and exist only to bring about death for whatever purpose they desired at the time of death.
Goals typically include death of a blood line, or of people who laughed at them, people who do a certain act, really anything that might have annoyed them in life or is related to their death could be a target.
Hunting a spectre involves finding out a lot of good information about the person they were as they are so interconnected to their former lives. Knowing how they died and what they did in life will greatly increase your chances of defeating them. As well they are one of the few types of undead where indiscriminate property damage is advisable. burning down the former doll maker's out int he middle of nowhere workshop where he tried to make a living doll will greatly improve your ability to destroy it. Not only was the bulk of their connection there, they might become frightened enough to go into hiding for a while. This allows you to regroup, study more and hunt down their remaining parts with little interference. also, it's pretty satisfying.
Each Spectre is highly unique, so general advice is hard to come by, however for fending them off most weapons tat handle ghosts will work to hold them off but will never be enough to destroy them. Learning what needs to be true for them to kill is also important, it it takes physical cues rigging a system where that possibly happen is a good idea, for example clamping your mouth shut to not scream or laugh when seeing it.
Just because it has gone dormant doesn't mean you have defeated it is an important thing to remember. Spectres, while driven by revenge, aren't stupid. hiding because a arsonist is trying to destroy them is a very solid plan from their end. short of any kind of magic, discovering what they have made and trying to trace it down is the best bet when they seem to have been defeated. They will typically still move to defend the last parts of them, and are just as powerful with one functional connection as they would be with all of them so do not assume you have them nessarily on the ropes. however, with fewer resources their available actions are a bit more liited, and unless they have the ability to connect to more after death you can leave them in a reduced state for some time before they even attempt revenge again.
In summary, Spectres are a diverse bunch, require learning about their life before death, and can be largely solved by large amounts of property damage.