Phasmophobia contains 24 different types of ghosts at this point in time. This can make the game pretty overwhelming for a new player trying to identify what makes each one tick. Below I will outline each specific ghost type, what their special abilities are, and how to test for whether the entity you are currently facing is one of these.

The Basic ghost. A Spirit can be determined by getting EMF level 5, Spirit Box, and Ghost Writing.
When smudging the ghost room of a Spirit, the Spirit will be unable to hunt for a full 180 seconds after you are done smudging.
It has a normal hunting speed, but speeds up gradually over time when it has line of sight of you

TEST:
To test for a Spirit, cleanse the ghost's room with an Incense after a hunt and set a timer. If the entity takes a full 180 seconds (3 minutes) before attempting to hunt again, odds are it's a spirit.

The Natrophobic ghost. The Wraith can be located with DOTS, EMF level 5, and Spirit Box evidence. The Wraith floats above the ground and will never step in salt piles that you place down. The Wraith also has a special ability that allows it to instantly teleport to a random player in the building, even outside the ghost's room. When using its teleport ability, it will leave a residual EMF 2 reading on the player it teleported to.

TEST:
To easily test for a Wraith, place several piles of salt around the ghost's room. If the entity never touches the salt piles, it is a Wraith.
As a more complex and harder test, you can wander to a room far away from the ghost's room and hold an EMF reader out. If you randomly get an EMF 2, it is a Wraith.

The Camera-Shy ghost. The Phantom can be located with DOTS, Ultraviolet, and Spirit Box evidence. The Phantom is very camera shy. When doing a visual ghost event, taking a photo of the Phantom will make it instantly disappear. The Phantom also has a tendency to wander, even outside the ghost room, towards a random player. While hunting, the Phantom blinks out of sight for longer periods of time than other entities, making them very hard to see during a hunt.

TEST:
To test for a Phantom, wait for a ghost event where you can see the ghost, quickly take a picture of the ghost while the event is still going on. If the ghost disappears when you take the picture, it is a Phantom.

Alternatively, while in chase and looping the ghost during a hunt, if you have a hard time seeing the ghost because it blinks out of sight for longer periods of time, odds are it's a Phantom.

The Tantrum ghost. A Poltergeist can be determined with Ultraviolet, Ghost Writing, and Spirit Box evidence.
The Poltergeist's special ability is it can perform a "Super Throw" where it launches multiple objects at the same time.
During a hunt, a Poltergeist has a 100% chance to throw an object every 0.5 seconds. Any time a Poltergeist throws an object, it drains 2% sanity from any players nearby.

TEST:
To test for a Poltergeist, build a pile of throw-able objects in the ghost's room. If the pile explodes with multiple objects being launched at the same time, it is a Poltergeist.

The Hunting ghost. A Banshee can be located with DOTS, Ultraviolet, and Ghost Orb evidence. The Banshee will choose a random player and make them its "Target". During a hunt, the Banshee will only attack the chosen "Target" player, and will ignore all other players it finds.
When gathering parabolic microphone evidence, the Banshee will give a very unique "Scream" unlike any other paranormal sounds. The Banshee is also more likely to do a singing ghost event.
If the "Target" leaves the building (goes outside or into truck), the Banshee will hunt normally like any other ghost.
If the "Target" dies by any means, the Banshee will pick another player to become the new "Target".
Additionally, the Banshee is the only ghost type that will base its ability to hunt off of its Target's sanity, and not the group's average sanity.

TEST:
To test for a Banshee, use the parabolic microphone to try and get its unique "Banshee Scream". The scream has a rare chance to happen, and is not guaranteed every time you hear something with the para-mic.

An alternative test for Multiplayer: Have each player in a different area of the building. Wait for the ghost to hunt, and see if it will ignore anyone in particular.

The Power-Hungry ghost. Can only use it's ability if the fusebox is ON.
You can locate a Jinn with EMF level 5, Ultraviolet, and Freezing Temperature evidence.
The Jinn is the only ghost that CANNOT turn off the building's fusebox.
A Jinn can instantly remove 25% of a nearby player's sanity. When it does this, it will leave a residual EMF 2 at the fusebox.
While hunting, once the Jinn gets line of sight of a player, it will speed up very quickly until it gets close to the player, when it will slow back down to a normal hunt speed. This will only happen if the building's power is turned on.

TEST:
To test for a Jinn, place an EMF reader at the building's fusebox. If you get a random EMF reaction from the fusebox (assuming it is not in the ghost room), it is a Jinn.

Additional Test: While hunting, watch the ghost's speed. If it quickly speeds up when it sees you, but slows down when it gets closer to you, it is a Jinn.

Reverse Jinn Test: After completing the first speed test during a hunt, turn of the building's power and wait for another hunt. If this time, the ghost doesn't change speeds at all when it sees you, it is a Jinn.

The Photophobic ghost. A Mare can be located with Ghost Orbs, Ghost Writing, and Spirit Box evidence. The Mare has the unique ability to instantly turn off a light switch as soon as you turn it on. Mares are also more likely to do a "light break" ghost event, which will permanently break the lights inside the room the event happened in. If you keep the lights on inside the ghost's room, the Mare will frequently wander outside the room away from the lights. The Mare is the only ghost in the game that CANNOT turn on a room's light.
The Mare may frequently turn off the fusebox to the building.
Mares can hunt at 60% average sanity if it is in a dark room, and 40% average sanity if it is in a lit up room.

TEST:
If you repeatedly turn on the light switch in the ghost's room, it may immediately turn it off, this is a Mare.
Additional Test: keep lights on near the ghost and ghost room. If it waits to hunt until you are below 40% average sanity, it is most likely a Mare.

The Speedy ghost. It can be located with Freezing Temperatures, Ghost Orbs, and Ghost Writing evidence.
The Revenant is very slow during a hunt when it does not have line of sight of a player. Once it gains line of sight, it will speed up very quickly and continue at that pace until it loses line of sight.

TEST:
Choose a long hallway or choke point and wait for a hunt. If you hear the ghost moving slowly before it sees you, and once it has line of sight it instantly speeds up and stays at that speed, it is a Revenant.

(Not to be confused by a Jinn's ability which speeds up with line of sight but slows back down when within range of a player. See "Reverse Jinn Test")

The Shy ghost. Shades can be located with DOTS, Freezing Temperatures, and Ghost Writing evidence.
The Shade will refrain from doing many visible ghost events, but can rarely still do them. The Shade will not interact with as many objects while players are nearby.
The Shade is INCAPABLE of hunting while a player is in the ghost's room.
A Shade can only hunt if the average sanity is below 35%

TEST:
If the average sanity is below 50% and the ghost waits to hunt until it gets below 35%, it is a Shade.

Additional Test: Wait inside the ghost room. If the ghost refuses to hunt while you are inside the room, it is a Shade.

The Aggressive ghost. Demons are located with Ultraviolet, Freezing Temperatures, and Ghost Writing evidence.
A Demon can begin hunting when the average sanity reaches 70%, however it has a rare chance to hunt at ANY sanity level, even 99%.
A Demon can hunt every 20 seconds, instead of the usual 25 seconds.
When placing a crucifix on the ground, the crucifix will have an additional 2 meters of range of effect on a Demon.
Cleansing the ghost's room, or near the ghost, will only prevent a Demon from hunting for 60 seconds; as opposed to the standard 90 seconds for other ghosts.

TEST:
If the ghost hunts or attempts to hunt at any point above 65% sanity, it is a Demon. (with one exception, see "Yokai").

Additional Test:
Place crucifix in a more central location of the ghost room. If it seems that the crucifix is being burned more easily, it is most likely a demand.

Additional Test: Cleanse the ghost room with incense and set a timer. If the ghost hunts before 90 seconds, it is a Demon.

The Sanity ghost. Yureis can be located with DOTS, Freezing Temperatures, and Ghost Orbs evidence.
A Yurei has an ability to touch or move a door twice in a row instantly.
When cleansing the ghost's room with incense, the Yurei will be trapped inside that room for a full 60 seconds.

Special Ability:
The Yurei can instantly remove 15% sanity from a nearby player. When it uses this ability, it will FULLY shut a nearby door.

TEST:
Open all doors in the building, (or near the ghost's room). If a door FULLY closes from being wide open, check your sanity. If your sanity dropped by a full 15%, it is a Yurei.

Additional Test: If the same door gets touched or moved twice in a row back to back, it is a Yurei.

The Main-Character ghost. An Oni can be located with DOTS, EMF level 5, and Freezing Temperature evidence. An Oni is not able to do a "ghost air ball" event (Loud breath in your ear and visible air ball floating towards you).
Onis tend to interact with their environment more frequently than other ghost types.
An Oni will be very visible during a hunt and will not blink out of sight as often.

TEST:
While in chase during a hunt, keep an eye on the ghost. If you can see the ghost during the chase for more than usual, it is an Oni.

The "Dumb and Deaf" ghost. Yokai's cannot sense a player's voice or equipment unless it is within a 2.5 meter range of the player.
A Yokai can be located with DOTS, Ghost Orbs, and Spirit Box evidence.

A Yokai does not like players talking, and can initiate a hunt at 80% average sanity or below if a players talks while within a 2.5 meter range of the ghost.

TEST:
Place a crucifix on the ground of the ghost room. Place salt piles or a motion sensor around the crucifix. Once the ghost steps in the salt pile, or activates the motion sensor, talk to the ghost in game while within 2 meters of it. If the crucifix burns, or it instantly hunts, it is a Yokai.

Additional Test: During a hunt, try talking or keeping your flashlight turned on. If it seems like the ghost doesn't know you are there, it is most likely a Yokai.

The Chilly ghost. Hantus can be located with Ultraviolet, Freezing Temperatures, and Ghost Orb evidence. While playing on reduced evidence type settings, the Freezing Temperatures will be a FORCED evidence type.
A Hantu, similar to a Mare, has a more frequent chance to turn off the building's fusebox.
Hantus increase their run speed during a hunt when they are in a cold room. Alternatively, if the Hantu is hunting through a warmer room, it will be much slower.
If the building's fusebox is turned off, and a Hantu is hunting, you can see a cold breath coming from the Hantu as it hunts.

TEST:
Hide in a closet or hiding spot during a hunt. Listen to the footsteps of the ghost. If it changes speed randomly (or multiple times) during the hunt, it is a Hantu.

Additional Test: (High risk) Turn off the building's power. Get into loop/chase with ghost. If you can see a cold breath of air coming from the ghost during a hunt, it is a Hantu.

The Boring ghost. Goryos can be located with DOTS, EMF level 5, and Ultraviolet evidence.
The Goryo is the only ghost in the game that CANNOT change its ghost room.
Additionally, you will only be able to see the DOTS evidence through a video camera, and while not in the same room as the ghost.

TEST:
If the ghost room has changed even one time, it is NOT a Goryo.

Additional Test: Place DOTS on ground in front of a video camera. Wait in room for DOTS evidence. If you never see DOTS while in the room, go out to the truck and watch the DOTS through your video camera. If you then are able to see DOTS evidence, it is a Goryo.

The Quiet ghost. Mylings can be located with Ghost Writing, EMF level 5, and Ultraviolet evidence.
Mylings tend to respond more frequently than other ghosts while you are using a parabolic microphone.
You can only hear a Myling's footsteps or noises within a 12 meter range, as opposed to a normal range of 20 meters for other ghost types.

TEST:
Hide in a closet or hiding space, place flashlight, TURNED ON, on the ground in front of you (This will not attract the ghost if it is not in your hands). Wait for a hunt. Pay attention to the sounds of the ghost versus the flickering of your flashlight. If the sound of the ghost walking or talking goes away before the flashlight stops flickering, it is a Myling.

The Pyrophobic ghost. Onryos can be located with Ghost Orbs, Freezing Temperatures, and Spirit Box evidence.
Onryos are scared of fire, and will not hunt when within 4 meters of a lit firelight.
Onryos have a higher chance to blow out a nearby lit candle or firelight.
If an Onryo blows out 3 firelights within a short period of time, it will be able to hunt at any sanity level.

TEST:
Place lit firelights directly next to a placed crucifix within the ghost room. If the ghost starts a hunt or burns the crucifix BEFORE blowing out the firelight, it is NOT an Onryo.

Additional Testing: Place both crucifixes in the ghost room. Place several lit firelights within a perimeter around the room. If the firelights get blown out and immediately the crucifix burns, it is an Onryo.

The Sibling ghost. Twins can be located with EMF level 5, Freezing Temperatures, and Spirit Box evidence.
The Twins have the ability to perform 2 separate ghost interactions at the same time, (i.e. throwing an object and moving a door at same time). When performing 2 interactions at the same time, the activity monitor will show a unique curvature (SEE ATTACHED PHOTO)


When hunting, the Twins will only send one of the siblings to hunt. One Twin is slower than the average ghost, the other is slightly faster than the average ghost. They can alternate between the fast Twin or the slow Twin each time it hunts, but cannot switch mid hunt, and is not guaranteed to switch, (can be slow twice in a row, etc.).
Twins have a higher chance to start a hunt from a different room than the ghost's room.

TEST:
Hide in closet or hiding space for at least 2 hunts. If the speed of the ghost during the hunt is different in one hunt vs. another, it is Twins.

The Powerhouse ghost. Raijus can be located with DOTS, EMF level 5, and Ghost Orbs evidence.
A Raiju draws power from your electronic equipment. During a hunt, a Raiju will disrupt your electronic equipment from farther than a normal ghost. A Raiju will be normal walking speed during a hunt until it is within range of electronic equipment. Once it gets within range of your equipment, it will instantly speed up.
A Raiju can initiate a hunt at 65% average sanity or lower if within range of electronic equipment.

TEST:
Place DOTS in an area that you are comfortable looping/chasing the ghost in. Wait for a hunt. If the ghost has a normal speed and then gets within range of the DOTS and INSTANTLY speeds up around the DOTS, it is a Raiju.

Second Test:
Remove the DOTS from the looping/chase area, and repeat the test, if the ghost does not increase speed this time, it is a Raiju.

The Shapeshifting ghost. Obakes can be located with EMF level 5, Ghost Orbs, and Ultraviolet evidence.
While playing on reduced evidence type settings, Ultraviolet will be a FORCED EVIDENCE.
Obakes only have a 75% base chance of leaving ultraviolet handprints, fingerprints, or footprints, as opposed to the 100% chance of other ghosts. When leaving handprint evidence, it has a rare chance to leave a 6 fingered handprint instead of a normal 5 fingered handprint.
During a hunt, an Obake has a 6% chance to shapeshift ghost models every time it blinks out of vision.

TEST:
Get into a loop/chase with the ghost during a hunt. Keep an eye on the ghost during the chase and watch for it to change ghost models or textures.

Additional Test: If you locate a 6 fingered handprint on a door or window, it is an Obake.

The Mocking ghost. Mimics can be located by Ultraviolet, Freezing Temperatures, and Spirit Box evidence. Mimics will ALWAYS have an extra evidence type, the Ghost Orb. This Ghost Orb does not count as real evidence, and will follow the Mimic while it wanders, even outside the ghost's room.
The Mimic's Ghost Orbs will be visible even on zero evidence settings.
The Mimic can pretend to be any other ghost type in the game, and can mimic different ghost types over time. (i.e. it can wander its room as a shade, but hunt as a Thaye). A Mimic can be very hard to determine, and very lethal.
A Mimic will mimic a different ghost type every time it hunts.

TEST:
If playing on 3 evidence, you will get 3 evidence AND Ghost Orbs.
If playing on 2 evidence, you will still get 3 evidence.
etc.
If playing on ZERO evidence, and you still have Ghost Orbs, it is a Mimic.

Additional Test:
Keep an eye on the Ghost Orbs. If they ever leave the ghost's room, but the ghost's room did not change. It is a Mimic.

Additional Test:
Pay attention to how the ghost behaves during a hunt, (i.e. how it sounds, how fast it is, etc.).
If each hunt is different, you are probably dealing with this tricky guy.

The Cursing ghost. Morois can be located with Ghost Writing, Freezing Temperatures, and Spirit Box evidence. The Moroi will place a curse on a player if it responds through a Spirit Box or a Parabolic Microphone. When a player is "cursed", they will lose sanity twice as fast as normal. Taking sanity medication, will remove the curse from the player.
Smudging the ghost with Incense during a hunt, will blind the Moroi for double the amount of time that the incense would blind any other ghost.
The Moroi will be faster during a hunt, the lower the average sanity is. (i.e. average sanity at 35% - 50% = slower/normal ghost pace, average sanity at 0% - 25% = much faster ghost pace during a hunt)

TEST:
If you get a response through a Parabolic Microphone, keep an eye on your sanity. If it seems like you are losing sanity faster than usual, take some Sanity Medication. If you start to lose sanity slower after taking the medication, it is a Moroi.

Additional Test: Try to get the ghost to hunt right below 50% sanity. Listen to the speed of the ghost during this first hunt.
Continue the process, and if the ghost's speed continues to increase with each hunt, as you are losing sanity, it is a Moroi.

The Hide and Seek ghost. The Deogen can be located with DOTS, Ghost Writing, and Spirit Box evidence. While playing on reduced evidence type settings, the Spirit Box will be FORCED EVIDENCE.
The Deogen has a unique respond with the Spirit Box that sounds like a very calm growl.
Deogens know where ALL players are AT ALL TIMES.
Do not attempt to hide if you think the ghost might be a Deogen.
When hunting, the Deogen will move incredibly fast while far away from a player. When it gets close to a player, it will slow down drastically and can be outrun even while walking. This reduction in speed is very noticeable and is the slowest ghost in the game (one exception, see Thaye).

TEST:
If you are able to get Spirit Box evidence, try listening for its unique breath-like growl response.

Additional Test: (More reliable)
Get into a chase with the ghost while it is hunting. If it runs up to you very fast and then instantly slows down to a snails pace, and cannot catch you even while you are only walking, it is a Deogen.

Again, this reduction in speed is VERY noticeable, and impossible to mistake.

The Aging ghost. Thayes can be located with DOTS, Ghost Writing, and Ghost Orbs evidence.
The Thaye starts off the game with an Age of 0. For every 2 minutes a player spends near the ghost in the ghost's room, the Thaye will Age by 1. This continues up to a maximum of 10.
At age 0, the Thaye is incredibly fast and will easily catch up to a player during a hunt.
As the Thaye ages, it's speed will decrease. At age 10, the Thaye will be as slow as (if not slower) than a Deogen.
The Thaye is also the only ghost type in the game that will change it's answer when a player asks "How Old Are You" on a Ouija Board. (i.e. age 1 Thaye will respond with 5, repeating the questions at age 5 will respond with a higher number like 25)

At age 0, a Thaye can begin hunting once the average sanity reaches 75%. For every 1 additional age value, this sanity threshold decreases by 6%. An age 10 Thaye can only hunt if the average sanity is below 15%.

TEST:
If the ghost begins a hunt while average sanity is above 65% and the ghost moves very fast, survive the hunt and try again after attempting to age the ghost. If the ghost's speed gets slower with each hunt, all the way down to a slow walking pace, it is a Thaye.

Additional Test: (If Ouija Board is present)
Ask the ghost "How Old Are You", and get it's response. Wait a few minutes and ask the same question. If you get a higher response, it is a Thaye.

I hope this guide has helped. Whether you are a newer player just checking the game out for the first time, or a more experienced hunter who still struggled to figure it out with less evidence.
There may be things that I have overlooked in this guide, and everything is subject to change as more updates come out.