D&D 5th Edition Data Explorer

Fear Aura
Any creature hostile to the pit fiend that starts its turn within 20 feet of the pit fiend must make a DC 21 Wisdom saving throw, unless the pit fiend is incapacitated. On a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to the pit fiend's Fear Aura for the next 24 hours.
dc:
dc type:
WIS
dc value:
21
success type:
none
Magic Resistance
The pit fiend has advantage on saving throws against spells and other magical effects.
Magic Weapons
The pit fiend's weapon attacks are magical.
Innate Spellcasting
The pit fiend's spellcasting ability is Charisma (spell save DC 21). The pit fiend can innately cast the following spells, requiring no material components:
At will: detect magic, fireball
3/day each: hold monster, wall of fire
spellcasting:
ability:
CHA
dc:
21
spells:
Detect Magic
usage:
type:
at will
Fireball
usage:
type:
at will
Hold Monster
usage:
times:
3
type:
per day
Wall of Fire
usage:
times:
3
type:
per day