Shapechanger. The mimic can use its action to polymorph its surface to resemble a spellbook. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Adhesive (Object Form Only). The mimic adheres to anything that touches it. A Medium or smaller creature adhered to the mimic is also grappled by it (escape DC 12). Ability checks made to escape this grapple have disadvantage.

Bookkeeper. While the mimic has at least 1 hit point, its pages and anything written on them can’t be damaged and don't deteriorate with age.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary book.

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

Mimic Spell.  The mimic contains 3d4 + 3 random spells from the wizard spell list.  It can can cast a spell written on its pages as though from a spell scroll.  Spells above 3rd-level are considered to be of a higher level than the mimic can normally cast.  Whether the mimic succeeds or fails in its spellcasting attempt, once it attempts to cast a spell written on its pages, it can't attempt to cast that spell again until it finishes a long rest.

Pseudopod. Melee Weapon Attack: +3 to hit, reach 0 ft., one creature holding the mimic. Hit: 3 (1d4 + 1) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 1) piercing damage plus 2 (1d4) acid damage.

Book Throw. The mimic hurls itself at space up to 20 feet away.  If that space is occupied by a creature, that creature must succeed on a DC 12 Strength or Dexterity saving throw (target's choice) or take 3 (1d4 + 1) bludgeoning damage and be knocked prone.  On a successful save, the creature takes no damage, isn't knocked prone.