These are all ‘types’ of spirits, rather than individual ones, so it is possible to meet many variants of the spirits briefly described here.
Note also the many linked on the bottom, that fit easily into Spirit World.
More spirits will follow yet.
Additional Ideas (7)
Their joined power building a strong foundation to rest on, known individuals could be still called upon for assistance, best by their closest family and friends. But when the memory of an individual fades away, the spirit will be slowly drawn deeper into the spirit group... replaced by the next generations to be called upon for assistance.
As the tribes of old have fallen apart, the contact with tribal spirits has been severed, the names to be called forgotten, and the tribal spirits themselves have changed. Some distinct family clans still have similar spirits near to them, but even their time seems to be over.
The Flyers - a type of a Traveller, those rare few who so strongly wished to fly, that they learned it here on their own, or merged with bird spirits. It is typical for them that they never land, but forever fly the skies of Spirit World, never stopping, always looking for another view, and another wind. Later, some of them actually become or merge with spirits of the winds.
The stars - true lovers, that have merged into one, and live only their eternal love, become stars on the sky, and are so clearly shining their devotion, that they are visible even in our world. Needing no one else, they are too distant to be contacted, though it is claimed they sometimes confer luck on lovers.
The Scary Ones are a sick folk, everyone agrees. Feeling little power during their lives, in a world of strange laws it can be easy to scare the living hell out of anyone, threaten and persuade others to do what they do not wish to do. But eventually, the victims free themselves of the scary presence, and learn to recognize the few tricks they have. This kind of spirits tends to travel in the opposite direction than most - loosing interest in spirits, they turn back to humans where there is limitless fun, and never a lack of 'spooky mansions' and 'cursed places'. They sometimes join genuine ghosts in their efforts, boring as they seem. Not rarely, they are chased off to this existence by other spirits.
The Scary Ones change in shape relatively quickly, shedding their boring appearances to become threatening shadows, monsters with many claws and teeth, and anything you can imagine. Still, somewhere deep is hidden the little clerk, or the quiet housewife...
These spirits did not accept what they have become, sometimes failing to notice their very death. The wondrous world of beauties uncountable is scary and alien to them, place where they cannot find a stable point to cling to. Instead they roam without purpose, or flee without a hope to ever stop. Communicating to them is very hard, bringing them to reason is close to impossible. Their best chance to find peace is to happen across the spirit herd of animals, running in fear of something, too familiar a state to not be joined. Later, when they calm down and stop, the one in their midst could be also drawn into this emotion... the few that have recovered from this state, found a way to normalcy, or have merged such a spirit group.
'The Nothing' - spirits that so much believe being of no consequence, that they get very close to be nothing. They make up the background of Spirit World, perhaps that is why it seems to be covered in a strange haze. If there is a more diffilcut thing that communicating with them, it is noticing them in the first place. It is said they know much but do not tell anyone.
The Broken are also well-known, and not for friendliness.
Some people are never content, nothing is good enough, or they never have enough, being too greedy, too wanting. Upon Death, all that was important before turns out to be nonsense, the new existence offering nothing comparable after this shock. Lacking a reason to exist, lacking a motive to do anything useful, or communicate with anyone, they withdraw into the deepest pits, and places where no one else wants to go, to wallow in pity, and suffer in self-loathing, hating everyone and themselves. There they would reside, lashing out at any visitor of chance, then fleeing; not of cowardice, but of the disgusting notion of sharing space with somebody else.
It is not unheard for mental diseases during life being ended by the spirit splitting into two or more. The Broken, in moments of greatest unrest, tear away parts of themselves so they do not have to cope with them. Inevitably, they produce many unstable, irrational, deformed beings that cannot be called sane, the originator hardly being different. It is said that when a necromancer creates an undead, they call upon these parts of souls - and they gladly oblige, feeling the pull of a similar soul and finally some purpose... but they turn soon to hate again, even against their new master, who they cannot hurt.
The Broken are probably the most loathed creatures in the Spirit World.
It is a frequent spirit to meet in the desolate places - an old, shuffling man (or woman), slowly making his way to an unknown destination, without a true purpose or hope. They have lost much of their original personality while still alive, due to the afflictions of age. Now they shuffle on, all the way to eternity. A few manage to recover, to regain a glimpse of former selves, or awake to a new existence... but that is too rare to be seen.
When encountered, they tend to have an air of disoriented friendliness, or unfocused hostility, but they don't respond to their surroundings, or attempts at communication. They can easily pass over to the other side, and back again, over and over... one day, they will shuffle through railway stations, and empty parks, ignored by everyone.
Death awaits the young and old. Sometimes children die, old enough to fend for themselves, not truly understanding what happened. If they avoid the more mature spirits, they will probably stay behind in their development, retaining their childish nature. They grow up with time, but there are always new ones, victims of accidents, violence, or even their curiosity.
Simple minded as they are, they tend to play pranks on others, show their tongues, or just be a general nuisance. A louder voice or a little scare will easily chase them away.