Skull Reaper (5e Creature)
From D&D Wiki
Gargantuan undead, chaotic evil
Saving Throws Dex +12, Wis +11
Vorpal Edge. The skull reaper's scythe attacks ignore resistance to slashing damage and score a critical hit on a roll of 19 or 20. In addition, critical hits made with the skull reaper's scythes deal four times the damage dice rather than two times the damage dice.
Death Attack (1/Turn). If the skull reaper has advantage on an attack roll, it deals an additional 17 (5d6) damage on a hit. In addition, if the skull reaper's attack is a critical hit, it removes a body part off the creature it hit with the critical hit (Roll 1d20 to determine the body part lost, reroll the 1d20 if the creature no longer has that body part). (1-7 arm, 8-15 leg, 16-20 head). (See Chapter 9 of the Dungeon Master's Guide for details on missing limbs.) If the target creature succeeds on a DC 28 Dexterity saving throw, it does not lose one of its limbs.
Spider Climb. The skull reaper can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Turn Resistance. The skull reaper has advantage on effects that would turn undead.
Magic Resistance. The skull reaper has advantage on saving throws against spells and other magical effects.
Lie in Wait. If the skull reaper stays still for at least 1 hour, it is indistinguishable from a large pile of bones.
Magic Weapons. the skull reaper's weapon attacks are magical.
Multiattack. The skull reaper makes three scythe attacks.
Scythe. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 21 (4d6 + 7) slashing damage.
Skull reapers are undead guardians of immense size and strength. The lower half of its body appears like a centipede, as numerous legs made of rib bones sprout from its long spine. Its torso is made up of different bones, and its two arms extend like some sort of preying mantis, but its scythes are much, much stronger. The head is long and alien, with a large mouth made up of three separate jaw bones, two split in half, and its empty sockets glow with red, nearly unnoticeable light. It makes quiet clicking sounds as it moves. Whether this is intentional or because of it's manufactured joints is unknown. Only the most powerful of necromancers dare to create this beast. Its menacing appearance causes weaker prey to flee, but the skull reaper's true power is in its dozens of legs, which propel it forward at incredible speeds. It often uses its magical ability to cling to ceilings and other structures to lie in wait for naïve explorers, and then descends upon them from above.
Adapted from 3.5 Homebrew wiki to 5e