Boss Encounter 16 - lvl 5 to 20

Glowing Deathclaw Large monstrosity , unaligned
Armor Class 18 Natural Armor Hit Points (15d20 + 35) Speed 50 ft., climb 50 ft., swim 50 ft., burrow 30 ft.
STR 24 (+7) DEX 20 (+5) CON 20 (+5) INT 10 (+0) WIS 14 (+2) CHA 1 (-5)
Saving Throws STR +11, DEX +9, CON +9 Skills Perception +8 Damage Resistances Bludgeoning, Piercing, and Slashing from Nonmagical Attacks that aren't Adamantine Condition Immunities Charmed, Frightened, Paralyzed, Petrified, Stunned Senses Passive Perception 18 Languages -- Challenge 12 (8,400 XP) Proficiency Bonus +4
Keen Senses: The Glowing Deathclaw has advantage on all Wisdom (Perception) checks.
Thermal Blind-sight: The Deathclaw can detect any physical object in front of it that is not behind cover as long as that object's exterior surface is of a different temperature than the surrounding environment. Such objects that are cannot hide from the Deathclaw. This detection does not rely on vision or sight and illusions or effects that only alter the appearance AMD not the physical shape of an object, like the seeming spell or invisibility, do not effect this detection.
Survival Instinct: When a Glowing Deathclaw starts its turn with 100 hit points of fewer, it enters an adrenaline-fueled frenzy and gains a +2 bonus to its AC, has advantage on strength and Dexterity saving throws, and can make and additional melee attack as part of their attack action. This effect last until the Deathclaw is slain or regains all of its hit points.
Evolved Claws: The Deathclaw attacks score a critical hit on a roll of 19 or 20.
Regeneration: The Glowing Deathclaw regains (1d6 +5) hit points at the start of its turn.
Actions Multiattack: The Glowing Deathclaw makes four attacks If two claw attacks hit the same target, the target must succeed on a DC 16 DEX saving throw or be grappled (escape DC 16 DEX) and restrained.
Bite: Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: (3d10 + 8) Piercing damage and (2d6) radiant damage.
Claw: Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: (3d10 + 8) Slashing damage and (2d6) radiant damage.
Gore: Melee Weapon Attack: +12 to hit, reach Grapple, one target. Hit: (3d10+ 6) Piercing damage and (3d6) radiation damage. If the Glowing Deathclaw succeeds on two Gore Attacks in the same round it will attempt to rip the target in half. The target must succeed on an opposed strength check or take (6d6 +12) (Magical) Slashing damage.
Tail Sweep: The Glowing Deathclaw its tail in wide arc. Each creature within a 15 feet of the Deathclaw must must succeed on a DC 16 DEX saving throw or take (2d8 +8) bludgeoning damage and be knocked prone.