Alter Reality

NOTE:  The caster must have a CHA of no less than 22 and an INT of no less then 21 to be able to comprehend and cast the intricacies of this spell.  

This ability stops short of the power a Wish spell can provide due to its specific nature, but is extremely potent nonetheless.  The caster creates an alternate reality from their own mind and then makes it so in the mind(s) of those targeted.  This spell requires 10 minutes of preparation time and cannot be cast as a ritual.

The spell psychically affects the minds of creatures within a 120' sphere into thinking they're in a reality / scenario different than the real world.  While their actual bodies remain where they stood before being affected, whatever world the caster dreams up occurs within the mind of those affected.  The created world is extremely convincing if those affected do not pass save throws as noted below.  The initial save throw is 10 + 1/2 the caster's level + the caster's CHA modifier.  A 20th level caster with a CHA of 22 creates a save throw of 26, as example.  Immunity from charm, illusion, or similar protections allow a save at advantage - but a save throw is required regardless.  Like Wish, there exists no 'blanket' resistance or immunity.

The spell lasts up to 10 rounds, where each round feels like 1 full day within the alternate world.  In simpler terms, while a creature feels it is in the created world for up to 10 days,  only 1 minute passes in the real world.  The spell does not require concentration. 

The affected creatures' bodies are vulnerable to attack, atmospheric effects, etc.  Any damage in the real world causes real damage to the creatures affected.  However, real damage allows affected creatures to make a save throw to break free of the alternate world.  Save throws are made at the end of each creature's turn.

Any damage experienced in the alternate world does not cause real damage to the affected creature.  However, should the affected creature die in the alternate world, the creature falls to 0 hit points in the real world.  Attempts to revive, cure, or resurrect the creature in the alternate world always fail.  The character must make death saves for their body in the real world.  A successful series of death saves grants the creature life, but with 1 hit point. 

For each real world round that passes, the character suffers necrotic "damage" (resistances fail, immunity cuts the damage by half, rounded down).  The damage reduces the affected creature's maximum hit points by the 2d10 points per round.  The damage does not cause pain or injury but does create a feeling of being tired while in the alternate world.  Only a Greater Restoration or Wish spell can reverse this effect.  Any creature's maximum hit points reduced to 0 or less suffers true death, only to rise as a Shadowguard (see Acererak’s Guide to Lichdom).

For each round a creature suffers the necrotic damage and subsequent max hit point reduction as mentioned above, they are permitted the CHA save throw as mentioned above (with advantage) to break free from the alternate world.  A creature who fails the save remains in the alternate world, feeling more tired the next day than the day before, still believing the created world is real.

Whether the spell ends or the creature breaks free from the spell, the round in which the create re-enters the real world ends their full round - no action, bonus action, reaction, etc.  Additionally, any affected creature's next initiative roll within 1 minute of real time is made at disadvantage.  As mentioned, any maximum hit point reduction is permanent unless restored by Greater Restoration or Wish.