So what do ghosts look like? There's not just one format for a ghost, there are countless ways a spirit can manifest itself to people and mediums.
Just like you and me...
Some ghosts look just like the living - and can be almost impossible to distinguish from afar. Up close you can usually see little strange flaws - for example (but none are usual): no pupils, flawless skin, just a bit see through, or even something as huge as no legs but they are walking as if they do have legs. Sometimes they can be missing arms or their eyes are off colour - colours that are unnatural like violet or fluorescent colours. But from afar they can look just so normal it's freakier than the ones that don't.
"Patchy" or Phasing
Sometimes they are patchy, in a way that DVD's skip.. you know, freezing, jumping ahead.. interruptions in visual and audio consistency.. they don't flow quite right. They can be a still image for a few moments then move all of a sudden. I've asked these spirits many questions about this phasing, and I find that these spirits are the more preoccupied ones. Ones with unfinished business, ones with worries galore. Oh ghosts worry so much it's a wonder people call them "at rest".
See-Through People
Sometimes they are translucent. This is the one most people associate with ghosts, in popular culture, lore, etc - the see-thru spirits that look like they're made of cloud or smoke or like they're halfway here and halfway "there". In my experience these spirits are in the same preoccupied category as the patchy spirits. The less visible and consistent they are, the more distracted or apathetic they are.
Abominations and Caricatures
Sometimes they exaggerate their forms, or try to take on a very scary appearance. They use their appearance in order to communicate a point. Scary looking ghosts, obviously, are trying to scare you. Already you have that in your list of advantages: you know this is either a desperate being or a childlike one looking for mischief. When a spirit is outrageous looking, they want attention. When they are super understated (no face, no details etc) the beings are grudgingly communicating or they hate taking the shape of a human - they hate who their species was in life or in the after life. When a spirit takes on the shape of a known character (be it popular entertainment culture, historical figures, or figures from your past) - that is a communication in itself. I've heard of people seeing spirits in the form cartoon characters. Anyways, this sort of exaggeration or under exaggeration is common, and many spirits decide to communicate this way. Sometimes this means that a loved one can look like someone entirely different at first, which I can't tell you how frustrating it is... I mean you describe Amelia Earhart to a daughter of a recently dead person and they kinda think you're either crazy or PT Barnum. I try to stay away from describing celebrities until I've had enough chance to see if the spirit is communicating something through its form.
Invisible
Some spirits do not portray themselves visually in any way. Not to the eyes, and not to the 6th sense's "eye". Emotions, words, sensation, and concepts can flow freely from these spirits without any visual information what so ever. I find these spirits can be the older ones, the ones that have been dead so long they don't quite care about visual appearance, it can get in the way of pure communication. These spirits can also be babies that were either never born or died when they were so small they had no concept of character form. It takes a while generally for children to get a good self-concept visually, so this can range from 0-3 years old depending on the development of the child.
Balls of Light!
These are my favorite. The most beautiful and feel-good energies usually. On average, these spirits are fetuses, unborn babies - or babies that died very early on. They can look like soap bubbles filled with light - a beautiful rainbow ring in certain lighting. They float without purpose sometimes, but they can also float with a purpose - such as guiding someone away from harm, or guiding them to something important to their security, destiny, or just to help them out or make them laugh.
Orbs
Some spirits take on a very similar form to the balls of lights - and that is "Orbs". The balls of light can be put into this category, but I wanted to separate them as I personally see a big difference. Orbs aren't so soap-bubble, and they don't have to be lights. Most orbs are not lights, but they reflect light amazingly well. Photography can be used to capture them to readily than the human eye, as the flash creates enough light to exaggerate them into view. They don't have to be perfect circles, I have seen oblongs, egg shapes, even jagged shapes. They range in colour but most of them are grey: plain grey, grey blue, grey green. I've even heard they come in pink! Lol! Although I'm not surprised, spirits are quite versatile. I have not been able to find a common factor between all orbs, no average type. They can be any walk of life, not just human. They can be animals too.
Their Corpses
The spirits that freak me out the most in terms of appearance are the ones that take the shape of their death - exaggerated or realistic. They will mostly do this as a way to communicate their method of death - some see it as a badge of honor, a mark of ascension, or a cross that they bear. Some spirits see it as a way to communicate what horrors happened to them, maybe because they want some kind of understanding, maybe because they want vengeance, and sometimes they want you to tell their story. Empathy goes a long way in the Spirit world. I won't go into detail, you get the picture.
I will add more types of spirit appearances later, including specific examples and perhaps sketches. I wanted to publish this to let you know I'm still out there and still ready to share and let you in on the world we should all be able to see!