The Corpse Ring is the prototype weapon of the Corpse Lantern. A standard Green Lantern ring is more 'Unlimited Power for a Limited Time'. Their rings can hold a charge which, in the past, would only last 24 hours, at which point they needed to recharge their rings from their portable lanterns, whereas Corpse Lantern Rings are like batteries that run out unless recharged. It is important to remember, though, that the Corpse Lantern ring is still every bit a Green Lantern ring. So any weaknesses the GL ring has, the CL ring has.
Founded by a rogue Guardian and commanded by Von Daggle, "The Corpse" is an elite, top-secret black ops division of the Green Lantern Corps (implied to include lanterns ressurected using rings or otherwise reborn, ala, literal corpse lanterns) and brainwashed to the point where the regular members of the Corps don't know about them; they spearheaded the one and only attempt to actually invade Apokalips, and continue to fight clandestine wars with Darkseid; and on and on. They are not restricted by the same rules that regular Lanterns follow, and they perform the darkest, most dangerous missions. Very few Lanterns are even aware of the existence of the "Corpse".
The Black Ops Division Edit
An elite, top secret, “Black-ops” division, “The Corpse” handle the darkest and most dangerous missions facing the Green Lanterns. The members of the Corpse follow different rules than normal Lanterns, and in fact most don’t even know of their existence. One example being that they were not bound by the use of Lethal Force even before the SCW. (Gardner mentioned during a mission with them that he’d never heard of the Corpse, and after the mission his memory of them was erased.) Not much is known about the Corpse, though what is known pertains simply to their duties. Members of the Corpse do not use power rings like most Lanterns; instead they are given coin-like disks which when swallowed give them all of the same abilities for a limited amount of time. The energy produced by these disks is purple, as opposed to the usual green (It could be that the light has been configured by the disks to be purple so as not to draw attention to the Green Lantern Corps., though with he revelations about the EES, it is unknown how this is achieved or what it signifies). Corpsemen do not wear the traditional green of other Lanterns, and under no conditions do they don the symbol. They tend to instead wear black uniforms that have no symbols, appropriate for their station. With the recent authorization of Lethal Force against Sinestro Corps members and other enemies of the Lanterns after the war, the need for the continuation of the Corpse is in question by some. Though their will likely remain a need for those who work in the shadows.
There were several notable differences between a Corpse Ring and a Power Ring. Corpse Lanterns are an elite within the elite. The chosen lanterns of the Foundation, drawn from only the most fiercely loyal. The Foundation, created Corpse Lanterns to perform missions too unsavory for the rank and file. Covert and clandestine of operations. To allow for this secrecy, they altered the color of their rings and removed their ethical reinforcement limiters. Thus, their operatives are able to perform whatever tasks they required of them, without inviting reprisal or bringing suspicion upon the Green Lantern Corps as a whole. However this level of obfuscation, this level of freedom requires a steep price, Those who join the Corpse Lanterns can never leave. Their rings can not be removed.
This is why they are called them the Corpse. Those who wear the ring... die... and live on only to serve Foundation. They are the perfect Green Lanterns. In fact, most Corpse Lanterns are already dead, or close to it, when they receive their new ring. They will live as long as the ring has power to sustain them and as long as they do their duty.