Temporal magic (chronomancy) is a difficult and dangerous thing, requiring many years of study and practice, an inherent grasp of the principles involved, and a great deal of luck. The Amulet (and it’s companion artefact, the Circlet) allow a mage to delve beneath the surface of the river of time and manipulate it. The effects can be deadly - and the side-effects can be earth-shattering.
The Amulet is designed to allow it’s user to control the forward movement of time. In practice, it has two distinct abilities:
Subjective Stimulation of Localised Time ("Drawing Time"):
The mage draws temporal energy from the area around him, focusing it upon himself. The objective effect of this is that the mage becomes incredibly fast, while those around him are slowed. The effect, like all those of the Amulet, is dependant entirely on the mage’s talent and knowledge, and can never be absolutely controlled, even by a grandmaster in chronomancy.
There are three variables used to decide the effect of this spell - the area of effect, the target effect, and the effect on the mage. For example:
Juliette, a mid-career mage, uses the Amulet to speed her actions during a battle. She extends the range of the spell to include everyone in her party, and the group of Orcs they are fighting - a sphere, fifty feet in radius. She warps the passing of time as much as she is able, slowing those around her by ten percent. That time is then applied to Juliette, speeding her actions by a factor of three for the duration of the spell.
Juliette has several options to later the effect of the spell - she can increase the temporal warping effect further, slowing all creatures in the area of effect by 50% while multiplying her own speed by twenty or thirty times. Alternatively, she can attempt to increase the area of effect, slowing a sphere which is two hundred feet in radius by 10%. Again, her own speed would be multiplied by a suitably enormous amount.
The example detailed above is actually a significant application of the powers of the Amulet - the vast majority of mages would be hard pushed to replicate the feat without falling foul of the Amulet’s side-effects (see below). Cara himself, the greatest expert in chronomancy, would be challenged to influence an area any greater than a thousand feet across by more than ten or fifteen percent - although such a warping of time would speed him by a factor of more than fifty.
Personal Temporal Vortex ("Rifts"):
The mage creates a rift in time, forcing his body and spirit into the future. In effect, the mage disappears and reappears at the end of the rift. The spell can cast the mage forward seconds, hours, days, or years - Cara himself has used this ability on many occasions to travel across centuries.
The two variables which influence success when using this spell are the length of the transit and the accuracy of the target. For example, Juliette, the mage who is becoming so proficient with the Amulet, could use it to transport herself one minute forward in time, perhaps to avoid an attack or a guard patrol. She would instantly disappear, only to reappear one minute later in the same spot, give or take a few seconds.
But if the fight was developing into a battle, Juliette might throw herself forward in time further. If she attempted a one-hour rift, there would be a greater chance of the period being longer or shorter than planned - several minutes in either direction. Attempting a rift which would last a week would result in inaccuracies of more than an hour. Cara’s use of the Amulet to transit across decades often resulted in him appearing weeks on either side of his target date - not that it mattered much too him. The accuracy of the transit is dependant on the expertise of the user. Should Juliette attempt a decade transit, she could easily be months off, if not a year.
Side-Effects of the Amulet:
As stated above, chronomancy is a dangerous and unpredictable sphere of magic. Side-effects of exceeding one’s abilities are varied, but uniformly unpleasant. Such effects include, but are not limited to: unexpected and sudden aging of the mage, subjective acceleration or deceleration, temporal instability - in worst cases, the mage can be cut adrift from time and vanish from this plane of existence altogether.
Juliette, our hapless volunteer, decides that, in order to save the kingdom from the Dark Lord, she must use the Amulet to increase her relative speed. Stretching her skills to breaking point, she manages to manipulate time over a wide area, hastening her actions many times over. The battle is short, and bloody. Too fast to be caught or defended against, Juliete butchers the Dark Lord where he stands. The spell abates, and time returns to normal.
Suddenly, Juliette falls to the ground, her hair grey and skin wrinkled, as if many decades have suddenly passed. Her condition is real, irreversible and possibly fatal in the very short term.
Like it’s companion item, the Circlet, the Amulet is a powerful and dangerous item which could give a PC the chance to substantially unhinge the campaign. Therefore, GMs should be warned that the items take years of study to use properly - an apprentice mage who stumbles across the Amulet and tries to use it risks scattering different parts of his body across millennia.