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 Circlet (and it’s companion artefact, the Amulet) 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 Circlet is designed to allow it’s user to control the backward movement of time. In practice, it has two distinct abilities:
Personal Temporal Vortex ("Rifts"):
This phenomenally potent ability allows the mage to travel backwards in time. This is extremely difficult and dangerous - moreso even than using the rift ability of the Amulet. In most cases, it is the work of a lifetime to master the Circlet sufficiently to create a stable rift, and even in those rare cases, travel into the past is dangerous.
Short journeys (less than an hour) can be completed by mid-level mages who are willing to risk their lives (see side-effects). After completing the spell, the rift will then deposit them in the same location, at the earlier time. The mage is then free to act, and interact, within that timeframe.
A short word on paradox. Time is a delicate thing, and will not endure temporal abuse by mages. For example, Juliette watches as her friend Layla is brutally slain by a Doom Knight. Overcome with grief, she uses the Circlet to create a rift, throwing herself ten minutes back into the past. She emerges from the rift into the same room, and sees herself and Layla fighting the Doom Knight. She enters the fray alongside her earlier self and Layla, but the Doom Knight is confused by her presence and switches his attention from Layla to the earlier version of Juliette. A moment later, the time-travelling version of Juliette watches her younger self being killed.
Paradox? Not at all. Time, unwilling to be so flagrantly mistreated, collapses completely into a localised temporal rift. The effects of such a rift are for individual GMs to decide - perhaps Juliette, Layla and the Doom Knight all wake up a few days later (or earlier) but are otherwise unharmed, or perhaps Juliette’s surviving party members have to complete an epic quest to close the rift before it consumes the entire universe.
Temporal Multiphasing ("Twinning"):
An unexpected application of advanced chronomancy is the ability to "twin" people or items. The Circlet allows the mage of warp spacetime, reaching into a possible future and pulling one person or thing back, to co-exist alongside it’s contemporary equal. For example, the Circlet could be used to duplicate an ally in the heat of battle, or create a duplicate of a valuable gem for nefarious purposes. The "twinned" person or item exists only for a short time, before the magic fades and it is returned to it’s original timeframe. The "original" also disappears, since it has now travelled back to the beginning of the spell.
For example, the players are approaching a difficult battle against a grumpy red Dragon. Juliette, a mid-level mage, uses the Circlet to "twin" Herbert, the party’s berserker barbarian. A second Herbert appears, and the two of them rush forward into battle. Juliette maintains the spell for as long as possible, but is finally exhausted after one minute. Both Herberts then disappear - the "twin" returns to the future, now one minute in the future, while the "real" Herbert has just been pulled back in time in order to fight Dragon. The balance in the skill is clear - if you duplicate an item for five minutes, then the real item disappears for five minutes after the spell has lapsed.
High-level chronomages (or those with no regard for their personal safety - see Side-Effects) can attempt to pull more than one future Herbert into the present. Juliette could stretch her skills to breaking point and pull four "twinned" Herberts into the present in order to give the Dragon a damn good talking-to. If the spell lasts for five minutes, then the party would be Herbertless for a total of twenty minutes thereafter.
The effort of maintaining a "twin" is draining - GMs should subtract health or mana for the duration of the spell to indicate exhaustion. When the caster lapses into unconsciousness, the spell abates. Living things are more difficult to twin than items, and large is more difficult than small. The "real" creature or item must be touched by the caster in order to be "twinned".
As a side-note - if the "real" object is destroyed or killed while it’s "twin" is present, both objects or creatures will be consumed in a temporal rift that could potentially destabilise time over a wide area. Twinning is not to be used lightly. If it is, GMs are encouraged to put on their Punitive Hat.
Side-Effects of the Circlet:
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 Circlet to "twin" her party’s Paladin. Stretching her skills to breaking point, she manages to pull together many disparate strands of time, recreating the mighty warrior many times over. The battle is short, the Dark Lord hacked into pieces by the vicious Paladins. The spell abates, and time returns to normal.
Suddenly, Juliette is gone, her temporal focus lost to the ravages of the spell. Her body and spirit pass forever onwards through endless time, witnessing the march of ages and the inevitable end of the universe, eternal and powerless.
Like it’s companion item, the Amulet, the Circlet 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 Circlet and tries to use it risks scattering different parts of his body across millennia.