Boss Encounter 8 - lvl 5 to 10

1x Guardian Naga Large monstrosity , lawful good
Armor Class 18 (Natural Armor) Hit Points (15d10 + 45) Speed 40 ft.
STR 19 (+4) DEX 18 (+4) CON 16 (+3) INT 16 (+3) WIS 19 (+4) CHA 18 (+4)
Saving Throws DEX +8, CON +7, INT +7, WIS +8, CHA +8 Damage Immunities Poison Condition Immunities Charmed, Poisoned Senses Darkvision 60 ft., Passive Perception 14 Languages Celestial, Common Challenge 10 (5,900 XP) Proficiency Bonus +4
Rejuvenation. If it dies, the naga returns to life in 1d6 days and regains all its hit points. Only a wish spell can prevent this trait from functioning.
Spellcasting. The naga is an 11th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 16, +8 to hit with spell attacks), and it needs only verbal components to cast its spells. It has the following cleric spells prepared:
Cantrips (at will): mending, sacred flame, thaumaturgy
1st level (4 slots): command, cure wounds, shield of faith
2nd level (3 slots): calm emotions, hold person
3rd level (3 slots): bestow curse, clairvoyance
4th level (3 slots): banishment, freedom of movement
5th level (2 slots): flame strike, geas
6th level (1 slot): true seeing
Actions Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one creature. Hit: (1d8 + 4) piercing damage, and the target must make a DC 15 Constitution saving throw, taking (6d6) poison damage on a failed save, or half as much damage on a successful one.
Spit Poison. Ranged Weapon Attack: +8 to hit, range 15/30 ft., one creature. Hit: The target must make a DC 15 Constitution saving throw, taking (10d6) poison damage on a failed save, or half as much damage on a successful one.