The derro is a 5th level spellcaster. Its spellcasting ability is Charisma (save DC 13, +5 to hit with spell attacks). The derro has the following paladin spells prepared:   1st level (4 slots): hellish rebuke, inflict wounds, shield of faith, wrathful smite   2nd level (2 slots): aid, crown of madness, darkness, magic weapon

Evasive. Against effects that allow a Dexterity saving throw for half damage, the derro takes no damage on a successful save, and only half damage on a failed one.   Insanity. The derro has advantage on saving throws against being charmed or frightened.   Magic Resistance. The derro has advantage on saving throws against spells and other magical effects.   Shadowstrike. The derro’s weapon attacks deal 9 (2d8) necrotic damage (included in its Actions list).