School: Chronomancy (Transmutation)
(Intended for use with the Chronomancer subclass)

Quick Description:
On casting...
- Pick a target creature within 60' (or self) : There are now two of the target creature, for the next minute.
- Roll percentile : base 30% chance that hostile creatures from the demiplane of time are summoned.
- Roll percentile : base 10% chance of Temporal Storm for each powerful/historically pivotal item duplicated.
On spell end...
- Flip a coin to pick a copy : that copy and all gear they appeared with vanishes.  Now only spells/charges/abilities the remaining copy used count as spent.
- Target makes Wisdom save vs base DC 15, or suffers Disadvantage on all rolls for 1d6 days.

Full Description:
There are now two of the target creature, for the next minute...  This dangerous spell causes a single target creature in range that the caster can see to begin to exist in two mutually exclusive states of probability, causing the target's lifeline to fork temporarily.  For the next minute, that creature exists in two places at once, each instance of it acting according to their own subjective perspective and circumstance, until reality is able to correct the anomaly.  Each instance of the target creature has all of their non-magical (see At Higher Levels for magic items effected with higher level slots) equipment and items, their unspent spell slots, and unused abilities.  Any magical items that were not bifurcated are evenly divided between the two creature instances as their controller sees fit, but must be decided upon immediately as the spell is cast.  Each instance of the target creature may use any or all of their independent resources, without effecting the quantity of the other instance.  Keep track of consumables, charges, spells, and abilities used separately for each instance of the target creature.  This is essentially like having a twin of the target creature for the duration of the spell, as well as a second piece of every affected item they were carrying when the spell was cast.

Control:
Both instances of the target creature share all initiatives, and are both controlled by the original character's owner (DM if NPC, Player if PC, etc), though the group may decide to allow two people to separately control each instance, with the owner's explicit permission, if it would simplify things or enhance fun.

Spell End:
One random copy, and all gear they started with vanishes; the other remains.  Only spells/charges/abilities the remaining copy used were spent...  At the end of this spell's duration, one of the two instances is chosen at random.  The selected instance and all their original bifurcated gear (regardless of who currently holds it) vanishes, and only the other instance now remains.  Only item charges, spells, abilities, consumables, damage, healing, status effects, afflictions, etc that the remaining creature has used or is suffering now apply.  (It may be helpful to refer to the copies as "Heads" and "Tails", "Evens" and "Odds", "High" and "Low", etc as soon as the spell is cast, to help track which copy vanishes when the spell ends.)

This spell ends prematurely if either of the creature instances is slain, destroyed, petrified, imprisoned (via the spell Imprisonment), or afflicted by any other similar character-ending effect.  If this happens, immediately select one of the two creature instances at random, as you normally would.  If the afflicted instance ends up being the one that remains, the creature is now suffering the affliction.

This spell also ends immediately if anyone casts Lifeline Bifurcation on a creature already affected by this spell.

Any non-bifurcated items that the vanished instance might have picked up or been given during the duration of the spell are left on the ground where they vanished.  Any duplicated items dropped or given to another character by the vanished instance before the spell ended vanish along with the creature.

Risks:
A base 30% chance that hostile creatures from the demiplane of time are summoned...  Casting this spell is a severe violation of the natural order of temporal mechanics, and essentially creates a short-lived, but very real paradox.  Much of the magic power of this spell is, in fact, spent simply containing this paradox so that it doesn't damage reality.  Large amounts of turbulence are created in the time-stream of the demiplane of time.  There is a 30% chance that this attracts the attention of some inhabitants of that demiplane.

A Base 10% chance of Temporal Storm for each powerful item duplicated...  Additionally, powerful or important items that get bifurcated by this spell carry a risk of inflating this paradoxical event to the point that it exceeds the spell's constraints and damages the fabric of reality.  The DM decides what items are famous, historically influential, or powerful enough to be considered "troublesome" should two instances of them exist simultaneously.  For each "troublesome" item bifurcated in this way, there is a cumulative 10% chance that a hole is torn in reality.  If this should happen, a massive Temporal Storm of tornadoes and mist-smoke will form, immediately pulling the caster, the target creature, and any living creatures within 100 feet of them out of reality, leaving them stranded in the demiplane of time.  Artifacts (allowed at higher level castings) are automatically considered "troublesome", unless the DM rules otherwise (such as might be the case for certain Chronomancer Artifacts).  Roll this probability as the spell is cast.

A Wisdom save vs base DC 15, or suffers Disadvantage on all rolls for 1d6 days...  Finally, when this spell ends, the target must make a Wisdom save to avoid long term scarring to their lifeline.  On a failed save, the target's fate is damaged, and as a result, they suffer Disadvantage on all rolls they make for the next 1d6 days.  This rotten run of luck due to damaged fate can be repaired at any time by spending all charges of the Lucky feat, by having Greater Restoration, Wish, or a similar restorative or reality-altering spell cast, or by spending an Inspiration token.  Otherwise, the damage mends itself naturally after the 1d6 days have elapsed.  Note: any character may spend their Lucky charges or use their Inspiration to heal another character's damaged fate.  The base DC for this save is 15.

The spell component is a tiny silver pitcher with two spouts.

At Higher Levels:
5th level slot - Common magic items on target are now also bifurcated.  Save at end of spell is DC 14.  Chance of Temporal Storm is 8% per troublesome item.
6th level slot - Uncommon magic items on target are now also bifurcated.  Save at end of spell is DC 13.  Chance of Temporal Storm is 6% per troublesome item.
7th level slot - Rare magic items on target are now also bifurcated.  Save at end of spell is DC 12.  Chance of Temporal Storm is 4% per troublesome item.
8th level slot - Legendary magic items on target are now also bifurcated.  Save at end of spell is DC 11.  Chance of Temporal Storm is 2% per troublesome item.
9th level slot - Artifacts on target are now also bifurcated.  Save at end of spell is DC 10.  Chance of Temporal Storm is 1% per troublesome item.

"Oh gods, now there are TWO of him!" - "Grumpy Gus", Dwarf Wizard

This spell is an original work.