Ice Devil

If the monster dies outside the Nine Hells, its body disappears in sulfurous smoke, and it gains a new body instantly, reviving with all its Hit Points somewhere in the Nine Hells.

The monster has Advantage on saving throws against spells and other magical effects.

The monster makes three attacks. It can replace one attack with a attack.

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The monster casts Wall of Ice (level 8 version), requiring no spell components and using Intelligence as the spellcasting ability (spell save DC ).

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Hit: damage. Until the end of its next turn, the target can't take a Bonus or Reaction, its Speed decreases by 10 feet, and it can move or take one action on its turn, not both.
Hit or Miss: The spear magically returns to the monster's hand immediately after a ranged attack.