Bixie's Soul Trap

 You attempt to trap the soul of a creature you can see within range in a gem, which serves as the material component for this spell. The creature must either be alive or have died within the last 24 hours.

Once cast, the targeted creature must make a Charisma saving throw.

• If the target creature is dead at the time the spell is cast on it, it automatically fails the saving throw.
• If the target creature has half of its maximum HP or greater, it makes the saving throw at advantage.
• If the target creature has max hp or greater, it automatically succeeds the saving throw.

The DC of the Charisma saving throw is determined by the value of the gem being used as the material component for the spell. The DC for the saving throw is 1, and it increases by 1 up to a maximum of 30 for every 100 gp the gem is worth.  Thus, a 1500 gp gem being used as the material component would require the creature to succeed on a DC 15 Charisma saving throw to resist Bixie's Soul Trap, and a gem worth 2800gp would require a DC 28 Charisma saving throw to resist. 

A creature that fails its saving throw enters a catatonic state. Its soul leaves the body and becomes trapped in the gem used as the spell's material component. On a saving throw success, the target resists the spell's effect, and any attempt to use the spell on this creature again for 1 hour automatically fails.

While the creature's soul inhabits the gem, it is aware of its surroundings as if in the gem’s space. It can’t move or use reactions.  The only action the creature is able to take is to attempt to return to its body.  It may attempt to do so at the beginning of each turn by succeeding the same Charisma saving throw described above, provided the soul is within 100 ft of its body and the body is not dead. The gem holds the trapped soul indefinitely or until the gem is broken, at which time the soul will automatically return to its body, provided the body is within 100ft and not dead.  If the soul can't return to the body, the creature will die. 

The material component of the spell is a valuable gem. The minimum value of the gem is:

• a gem worth at least 500gp if the target creature's max hp is less than 100;
• a gem worth 1000gp if the target creature's max hp is between 101 and 200; and
• a gem worth 1500gp if the target creature's max hp is 201 or greater

Higher level casting. When cast at a higher level, the saving throw DC for the spell increases by 2 for every spell level above 5th.