To successfully use Zaphkiel's Domain Expansion the caster must attempt a DC 25 intelligence check. On a failure the spell fizzles out, otherwise the spell has the following effect:

You rip a hole in the plane around you and impose a 60 ft radius demiplane taking it's exact place with. The area within a 120ft radius of you becomes Difficult Terrain. You can choose any number of creatures to be unaffected by this when you cast the spell. The inside of the demiplane appears to be an empty sphere 120 feet in each dimension, made of a nonmagical material and appearance of the casters choice. The caster can also modify the exterior of the demiplane to appear either reflective or completely opaque. If the wall of the demiplane cuts through a creature's space when it appears, the creature is pushed to one side of the wall (your choice which side). Nothing can physically pass through the wall of the demiplane from the inside. A disintegrate spell destroys a corresponding targeted 5ft portion of the wall instantly, however. Creatures may enter from outside of the space by willingly becoming subject to the effects of the spell. The wall also extends into the Ethereal Plane, blocking ethereal travel through the wall. When the spell ends, the demiplane disappears, and any creatures or objects inside the demiplane return to the position they occupied before entering.

All affected creatures within the demiplane are subject to the following effects:

• At the beginning of its turn the affected creature must make a succeed on a Wisdom saving throw or drop whatever it is holding and become stunned until the end of the round.
• Abilities, not spells, dependent on a specific god or deity such as Channel Divinity or Divine Intervention automatically fail.

As a Bonus Action on your turn you may target any number of affected creatures inside the demiplane to make a Charisma saving throw at disadvantage. On any failed save you may choose the effect of the demiplane on your target from the following options:

Summon Great Beast. You summon a CR 10 or below creature that you are familiar with which takes it's turn directly after yours, obeying your commands. The creature dissipates at the end of the round.

Grand Incantation. You cast a single target 7th level spell or below without expending a spell slot that targets the affected creature. If this spell requires a saving throw, target creature automatically fails that saving throw. If this spell requires an attack roll, it automatically hits. 

Reversal: Red. The affected creature takes 12d6 force damage.

At the end of each turn, beyond the turn that the spell was cast, that Zaphkiel's Domain Expansion is active the caster must make a DC 25 Constitution saving throw or take 1 level of exhaustion.

Only one instance of Zaphkiel's Domain Expansion can exist in a single space. If another creature casts Zaphkiel's Domain Expansion with an overlapping sphere to yours. the caster with the higher spell save DC has their domain overtake the others ending the weaker domains effects. Ties result in a contest of spell attack rolls, with the winners demiplane remaining in effect.