Boss Encounter 2 - lvl 5 to 10

1x Bone Devil Large fiend (devil) , lawful evil
Armor Class 19 (Natural Armor) Hit Points (18d10 + 60) Speed 40 ft., fly 40 ft.
STR 18 (+4) DEX 16 (+3) CON 18 (+4) INT 13 (+1) WIS 14 (+2) CHA 16 (+3)
Saving Throws INT +5, WIS +6, CHA +7 Skills Deception +7, Insight +6 Damage Resistances Cold; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks that aren't Silvered Damage Immunities Fire, Poison Condition Immunities Poisoned Senses Darkvision 120 ft., Passive Perception 12 Languages Infernal, Telepathy 120 ft. Challenge 9 (5,000 XP) Proficiency Bonus +4
Devil's Sight. Magical darkness doesn't impede the devil's darkvision.
Magic Resistance. The devil has advantage on saving throws against spells and other magical effects.
Actions Multiattack. The devil makes three attacks: two with its claws and one with its sting.
Claw. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: (1d8 + 4) slashing damage.
Sting. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: (2d6 + 4) piercing damage, and the target must succeed on a DC 14 Constitution saving throw or become poisoned for 1 minute plus take (3d6) poison damage. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.