Brazen Serpent

Magic Resistance. The serpent has advantage on saving throws against spells and other magical effects.

Bronze Embodiment. The serpent does not need to breath or eat. While the serpent remains motionless, it is indistinguishable from a bronze statue.

Spellcasting. The Brazen Serpent spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks).  

At Will:  detect evil and good, lesser restoration, spare the dying

1/day each: mass cure wounds, revivify, spirit guardians

Multiattack. The serpent can make two bite attacks.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 17 (3d8 + 5) piercing damage plus 4 (1d8) radiant damage. 

Radiant Presence. Each creature of the serpent's choice that is within 60 feet of the serpent must make a DC 16 Constitution save or take 12 (4d6) radiant and be stunned until the end of their next turn on a failed save or take half the damage on a successful save.

Coil. Bonus action on turn: The serpent coils its body, and gains +4 AC and an additional +4 to hit on its bite attack. While coiled the serpents movement speed is 0 and cannot be increased in anyway. These effects last until the serpent uses another bonus action to become uncoiled or falls unconscious.