Archiviathan

Spell Archive. Once per turn, when attacking with Fling Book, there is a chance that the Archiviathan throws a spell scroll instead if both of the damage dice have a matching result, which uses the point of contact as the spell's origin point and corresponds to the following spells based on the die result.
1 = shatter
2 = darkness
3 = entangle
4 = fireball

Multiattack. The archiviathan makes two attacks in any combination of Slam and Fling Book.

Slam. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.

Fling Book. Ranged Weapon Attack: +6 to hit, reach 30/60 ft., one target. Hit: 9 (2d4 + 4) bludgeoning damage. The archiviathan loses 1d4 HP if the book it flings is from its body.

Printstorm (Recharges on SR). While at or below half of its maximum HP, the archiviathan begins to lash out and immediately uses Printstorm instead of its normal attacks. Each non-Construct creature within 40 ft. must make a Dexterity saving throw. On failed save, each creature takes 4d10 slashing damage or half as much on a success.

Restoration (3/day). While at or below half of its maximum HP, the Archiviathan can use its bonus action to Dash toward a pile or shelf of books and reconstruct itself as part of that same action. This grants it 20 temporary hit points and consumes the books which were within the pile or shelf.