Book Golem
Large construct, neutral

Armor Class 20 (Natural Armor)
Hit Points 195 (20d10 + 75)
Speed 30 ft.

STR
24 (+7)
DEX
9 (-1)
CON
20 (+5)
INT
17 (+3)
WIS
11 (+0)
CHA
1 (-5)

Saving Throws CON +11, INT +9, WIS +6
Damage Immunities Poison, Psychic; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks that aren't Adamantine
Condition Immunities Charmed, Exhaustion, Frightened, Paralyzed, Petrified, Poisoned
Senses Darkvision 120 ft., Truesight 20 ft., Passive Perception 12
Languages Common This golem has absorbed language through the books that make up its body. It is able to speak and understand common.
Challenge 17 (18,000 XP)

Fire Fright Whenever the golem is subjected to fire damage, it must make a wisdom saving throw against a DC of 10 or half the damage received, whichever is higher.  On a fail, the Book Golem must move its full speed away from the source of the damage on its next turn.

Paper Body. If the Book Golem is killed by an attack that includes any fire damage, its body is consumed by magical fire.  The golem's body is destroyed, leaving a pile of burnt paper ash in its place.

Immutable Form. The golem is immune to any spell or effect that would alter its form.

Magic Resistance. The golem has advantage on saving throws against spells and other magical effects.

Magic Weapons. The golem's weapon attacks are magical.

 

 

 

Spellcasting.  The golem has absorbed various magical writings, spell scrolls, and energies.  It is able to cast the following spells.  The golem's spellcasting ability is intelligence, and has a spell DC of 18.

At will:  Acid Splash, Mage Hand, Light, Nystul's Magic Aura

3/day each: Fog Cloud, Magic Missile, Thunderwave

2/day each: Phantasmal Force, Suggestion

1/day each:  Slow, Fear

Actions
Multiattack. The golem makes two melee attacks.

Slam. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage.

Book Fling. Ranged Weapon Attack: +13 to hit, 30 ft. range, one target. Hit: 23 (3d10 + 7) bludgeoning damage.

Poison Breath (Recharge 6). The golem exhales poisonous gas in a 15-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 45 (10d8) poison damage on a failed save, or half as much damage on a successful one.

Reactions
Counterspell.  3/day the golem can cast Counterspell as a fifth level spell, using its reaction.

Legendary Actions
The Book Golem has two legendary actions, and regains all spent legendary actions at the beginning of its turn.

At the end of another creature's turn the Book Golem may use the following legendary actions:

Book Swarm. The golem makes a melee attack against one target within reach.  On a hit the target is restrained in the grip of the golem.  The target takes 2d6 slashing damage at the start of its turn, and may attempt to escape the grapple as an action with a DC 18 strength(athletics) or dexterity(acrobatics) check. (1 legendary action)

Cast a Spell.  The golem casts one spell from its list of spells. (2 Legendary Actions)