Time Stone

The Time Stone is one of the six Infinity Stones, the remnant of a singularity that predates the universe. It has the ability to manipulate time, even in places "beyond" time, such as the Dark Dimension. It was contained inside the Eye of Agamotto under the protection of the Masters of the Mystic Arts, who swore to protect it. Doctor Strange came across the relic and used it to force a bargain with Dormammu. Doctor Strange later relinquished the Stone to Thanos in exchange for sparing Iron Man's life.

Origins
When the universe was first born, the Cosmic Entities fashioned the remains of six singularities into concentrated ingots which became known as the Infinity Stones. As indicated by its name, the Time Stone held dominion over the forces time. The earliest known owner of the Stone was the sorcerer Agamotto who fashioned a containment device to better wield its awesome power. When Agamotto founded the Masters of the Mystic Arts, usage of the Eye became forbidden though Cagliostro was permitted to study the artifact and eventually wrote how to control the relic in his book. The Masters would subsequently swear an oath to protect the Time Stone with their lives.

Usage by Strange
During his training a Kamar-Taj, Doctor Strange began to read the Book of Cagliostro and learned of the Eye's full power. Seeking to push himself, Strange donned the Eye and opened it, revealing the Time Stone, before testing its power on his apple before using it to recreate the lost pages from the Book. He was halted by Wong and Karl Mordo who warned that the Eye's powers were contrary to the natural order of things and the slightest misuse could result in an endless temporal loop.

Dark Dimension
When the Hong Kong Sanctum was destroyed and the Dark Dimension began assimilating Earth, Strange used the Time Stone to rewind time only to be stopped by Kaecilius before the Sanctum could be fully restored. At wit's end, Strange flew directly into the Dark Dimension to confront Dormammu, trapping the being in a time loop that Strange would only break if Dormammu acquiesced to the human's terms. Dormammu eventually withdrew from Earth with Strange returning the Eye to its resting place in Kamar-Taj soon after where Wong causally revealed its true nature.

In Thanos' Possession
In early 2018, Bruce Banner returned to Earth to warn the planet of Thanos' imminent arrival. After meeting Strange and Wong, the three sought out Tony Stark for his aid who simply proposed destroying the Time Stone to derail Thanos' plans. As the four debated which action to take, Ebony Maw and Cull Obsidian arrived demanding the Time Stone. While the Earth heroes managed to defeat Obsidian, Maw managed to abduct Strange who revealed he had placed a spell around the Time Stone so that it could only be taken from him if he wished it so. Aboard Maw's Q-Ship, the torturer attempted to force Strange into surrendering the Stone only for him to be slain by Iron Man and Spider-Man. Though Strange wanted to head back to Earth, Iron Man convinced him Thanos would follow the Time Stone wherever they took it and that fighting him on Titan, away from any innocents, was the best course of action. Strange reluctantly agreed but warned he would sacrifice them all for the Time Stone if need be.

Upon arriving at their destination, the three were met by half of the Guardians of the Galaxy. As introductions were made, Strange used the Time Stone to examine over fourteen million possible outcomes of their inevitable battle with Thanos. In all but one, they would lose. In preparation for the Titan's arrival, Strange removed the Stone from the Eye of Agamotto and sent it to hide amongst the debris. In the subsequent battle, Thanos, while impressed by Strange's mastery of the arcane, soon deduced that he had parted with the Time Stone given that he failed to use its power against the Titan. When Thanos was on the verge of killing Tony Stark, Strange bartered the Time Stone for his ally's life. Inserting it into the Infinity Gauntlet, Thanos promptly took his leave to collect the Mind Stone.

Upon arriving in Wakanda, Thanos effortlessly made his way through the resistance but was too late to stop Wanda Maximoff from destroying the Mind Stone. Unfazed, he simply used the Time Stone to recreate the Mind Stone and completed the Gauntlet whereupon he was stabbed by a vengeful Thor. In spite of his wound, he managed to use all six Stones to wipe out half of all life in the universe. On Titan, Stark questioned why Strange had given up the Time Stone who cryptically stated there had been no other way before he vanished.

Capabilities
As the Infinity Stone that represents and governs over time, the Time Stone has absolute control over time and like with all Infinity Stones, is among the most powerful artifacts in all existence, with its power over time being so immense as to affect even a being as powerful as Dormammu. Due to its power, it cannot be held and used by anyone not powerful enough to withstand it, thus necessitating Agamotto to create the Eye of Agamotto as a container to allow other sorcerers to use it. Even then, the Time Stone's powers can easily prove too much for anyone who does not have the required knowledge and ability to use it, as it can very well kill anyone not skilled and powerful enough to use the Stone and can potentially prove dangerous for the natural order, due to it being able to break the natural flow of time and create alternate timelines. It can direct the flow of time, both backwards and forwards, and can even loop a section of it. This can be used to indirectly undo even death. If in a time loop, time will repeatedly reset to a set point until the loop is manually undone.

The Time Stone also allows the user to look into possible different futures at an incredible rate. The Ancient One was able to use it to peer through time and see future threats. Doctor Strange exploited this ability prior to the Battle of Titan, looking through over 14 million alternate futures, to find a way to defeat Thanos.

The Time Stone can also be used to restore damaged or destroyed objects, as shown when Doctor Strange reconstructed the torn pages of the Book of Cagliostro. These reconstructed pages appeared to be duplications of the originals, rather than the originals themselves, as they did not seem to possess the same dark magic.

However, it seems the Stone can truly recreate destroyed objects in other situations. For instance, Thanos used the Time Stone to reverse the Mind Stone's destruction (as well as Vision's death). This is potentially a result of the Stone being used in conjunction with the four other Infinity Stones Thanos possessed at the time.

Trivia

 * In the comics, the orange Time Gem manipulates time; can amplify or reverse aging; and allows the user to see, travel into, and/or change the past or the future.