Divine Sanctum/Infernal Colosseum

When you cast this spell, either infernal or divine magic roars from your body to force all creatures in the area into an arena of your patron's choosing.  A 60 foot radius sphere barrier of divine or infernal power forms centered on yourself. 

Creatures are incapable of physically passing through the barrier or teleporting outside of the arena by any means, even to another plane, including the ethereal.  A disintegrate spell cannot harm the barrier, a creature must succeed a DC 21 ability check to attempt to counter this spell, as opposed to the casting's normal DC, and the arena can not be dispelled by dispel magic. 

If a creature willingly moves into the space of the barrier from either side, they must succeed a Strength saving throw or be pushed 15 feet away from the barrier.  Lastly, you gain a bonus to Constitution saving throws equal to your spellcasting ability modifier. 

Creatures in the area are subjected to the following effects depending on which arena is chosen.

Divine Sanctum

• Up to eight creatures of your choice (chosen when you cast this spell) have advantage on attack rolls and ability checks.
• Up to eight creatures of your choice (chosen when you cast this spell) deal an extra 2d8 radiant damage on attack damage rolls.  Celestials chosen within the arena deal an additional 1d8 radiant damage.
• Up to eight creatures of your choice (chosen when you cast this spell) are resistant to necrotic and poison damage.  Celestials chosen within the arena are immune to these damage types.
• Creatures of your choice in the arena regain the maximum number of hit points possible from any healing.
• Creatures in the arena are immune to the frightened condition.
• Fiends and Undead must make a Charisma saving throw or have disadvantage on attack rolls, ability checks, and saving throws.  Creature's can repeat this saving throw at disadvantage at the end of each of their turns, ending the effect on a success.

Infernal Colosseum

• Up to eight creatures of your choice (chosen when you cast this spell) must succeed a Charisma saving throw or have disadvantage on attack rolls and ability checks, and can not regain hit points.  On a success, the creature does not have disadvantage on attack rolls and ability checks, and all healing received is halved.  Creature's can repeat this saving throw at disadvantage at the end of each of their turns, ending the effect on a success.
• Up to eight creatures of your choice (chosen when you cast this spell) deal an extra 2d8 necrotic damage on attack damage rolls.  Fiends chosen within the arena deal an additional 1d8 necrotic damage.
• Up to eight creatures of your choice (chosen when you cast this spell) are resistant to fire, necrotic, and poison damage.  Fiends chosen within the arena are immune to these damage types.
• Creatures in the arena have disadvantage on saving throws against the frightened condition.
• Fiends and Undead have advantage on attack rolls, ability checks, and saving throws.