Poe

A Poe is a spirit of concentrated hatred that freely roams graveyards and other haunted locales about Hyrule. They always carry some sort of lantern with them that serves as the container for that specific Poe's soul.

A Link to the Past
Poes originally appeared in A Link to the Past, filling the role Ghinis served in the first game. The original Poe behaved nearly identical to its predecessor, flying sporadically around gravesites and appearing from beneath disturbed tombstones. They also had unusually high endurance and health for a simple enemy. It is very similar to the Reaper in both behavior and appearance.

Ocarina of Time and Majora's Mask
In Ocarina of Time and Majora's Mask, Poes take on the appearance of hooded wraiths with glowing eyes, faces shrouded under their oversized cloaks. Their distinctive lanterns immediately identify them, even from a distance, and the Poe itself comes into view as Link approaches. Targeting Poes in these games will cause them to become temporarily invisible, although they will reappear in even, and predictable intervals. Their lanterns remain visible when they vanish allowing Link to at least dodge and keep track of the invulnerable enemy until it reappears. When a Poe is defeated, its physical body disappears, and the lantern it was holding drops and breaks, revealing its spirit. The Poe Spirit is a purple-flamed face that glows with melancholy, disappearing after a short while of inactivity. Before it disappears, Link can put the Spirit in a bottle, which is primarily used to sell for Rupees. Drinking it will usually recover health, but it can also damage Link as well.

Location
In Ocarina of Time, Poes are predominately found in Kakariko Graveyard and in Majora's Mask, they are found in the Stone Tower Temple. There are also ten Big Poes in Ocarina of Time that are scattered throughout Hyrule Field when Link is an adult. Big Poes can be easily hunted down on Epona and killed using the Bow from horseback. Once killed, their Big Poe spirits could be collected and sold to the Poe Collector in the gatehouse of Hyrule Castle Town; capturing and selling of 10 yields Link another Empty Bottle.

Notable Poes
There are four Poes known as the Poe Sisters: Joelle, Beth, Amy, and Meg. In Ocarina of Time, these Poes are the sub-bosses of the Forest Temple. They stole the four differently colored flames necessary to fight Phantom Ganon, and Link must defeat them in four separate battles to relight the torches. They are fought as a mini-game in Majora's Mask as well.
 * The Poe Sisters

To get to the Spirit Temple from the Gerudo's Fortress, Link needs to cross the Haunted Wasteland using a Poe, who can only be seen with the Lens of Truth, as a guide. Link must follow this Poe known as the Phantom Guide to reach the Spirit Temple.
 * Haunted Wasteland Guide

In Ocarina of Time, the ghosts of the royal Composer Brothers named Sharp and Flat tell Link about the Sun's Song after he defeats them in Kakariko Graveyard (Flat and Sharp fight like regular Poes, except for their ghosts are colored green after their defeat). In Majora's Mask, Flat rewards Link with the Song of Storms which is used to defeat Sharp later in the game.
 * Flat and Sharp

In Ocarina of Time, ten of these ghostly creatures haunt Hyrule Field. They only appear while on horseback. When Link spots one, it will run away so he must quickly defeat it with arrows. After being defeated, they can be bottled and sold to the Poe salesman. Capturing and selling all ten of them will earn Link another empty bottle.
 * Big Poe

In Majora's Mask, defeating the Big Poe at Ikana Graveyard earns Link an empty bottle, and defeating the one inside the Ikana Well allows him to give its captured soul to a Gibdo to proceed.

The Wind Waker
In The Wind Waker, Poes have a different appearance, masked with multicolored bodies. They harass Link by burning him with their lamps. They can also jump into Link's body, possessing him, and thereby reversing his movement controls. After the possession is over with, the Poe exits the body and it will disappear, as if it had been defeated. The Poes are now permanently translucent until direct light is shone on them using the Mirror Shield. The Poes will then become solid and run frantically about the room making them vulnerable. They appear in the Earth Temple and also inhabit the Ghost Ship, among other places. It is also said that Jalhalla, the boss of the Earth Temple, rules over all Poes.

Four Swords Adventures
A singular Poe appears as the core form of Jalhalla, king of the Poes. The only way to defeat him is to light four torches that make him vulnerable. He also spawns normal Ghinis.

Twilight Princess
In Twilight Princess, Poes take on a role similar to that of Gold Skulltulas in Ocarina of Time. A man in Castle Town named Jovani was cursed for his greed and had his soul stolen by "Imp Poes," of which there are a total of 60 throughout Hyrule. Imp Poes only come out at night and can only be defeated using Wolf Link's heightened senses. Once a Poe has been damaged, it will fall to the ground and its soul will become visible, which can be ripped out and collected by performing the Ending Blow on it while still in wolf form. Collecting 20 souls will break part of the curse on Jovani, and he will give Link a bottle full of Great Fairy's Tears as thanks. After all 60 souls have been collected, the curse will lift completely, and Jovani's cat Gengle will give Link 200 Rupees every time he enters the room thereafter, similarly to father of the family in the House of Skulltula, granting him a fast and unlimited source of money.

Of the 60 Poes in Hyrule, the four in the Arbiter's Grounds are of particular interest to theorists. Not only do they look and attack differently from regular Imp Poes, but their role of impeding progress to a certain area of the dungeon by stealing the fire from four torches is markedly similar to the behavior of the four Poe Sisters from the Forest Temple in Ocarina of Time, leading many to believe that they may be the same. This seems to be supported by the last Poe's strategy of duplicating itself and encircling Link, the same strategy used by Meg, the last of the four Poe Sisters.

Phantom Hourglass
The poes that appear aboard the Ghost Ship have a radically different look in comparison to their earlier counterparts. They resemble puffer fish with purple body markings, having floating tadpoles for arms. They attack by teleporting back and forth, periodically spitting a ball of blue fire at Link during this process. They can only be struck when visible and will actively avoid Link's attacks.

The Cubus Sisters more closely resemble the traditional Poe design as well, though they have not been confirmed to be Poes.

Etymology
It has been speculated that the name "Poe" was derived from the name of the famous poet Edgar Allan Poe who is known for his dark, gloomy works, though it could have also been named from the Chinese word "po" which means "spirit".

Trivia

 * An early beta design of the Imp Poe from Twilight Princess has been found.
 * In Majora's Mask, the aliens only known as "Them" bear a resemblance to Poes.