This spellbook looks like a completely ordinary tome, save that every so often it spontaneously sprouts eyes, teeth, and tendrils. When found, the book contains the following spells: alter self, animate objects, disguise self, seeming, shapechange, Tasha's caustic brew, and true polymorph. It functions as a spellbook for you.

While you are holding the book, you can use it as a spellcasting focus for your wizard spells, and you have advantage on saving throws against any spell or effect that would alter your form.

The book has 3 charges, and it regains all expended charges daily at dawn. You can use the charges in the following ways while holding it:

• If you spend 1 minute studying the book, you can expend 1 charge to gain the ability to instantly identify shapechangers for 1 hour.  Until the effect ends, you see a faint aura around any visible shapechanger within 60 feet of you, regardless of what form it is in.
• When a creature you can see within 30 feet of you is targeted by a spell or effect that would alter its form, you can expend 1 charge as a reaction to intercept the shapechanging magic, causing you become the target of the spell instead of the original target.  Alternatively, by spending 2 charges, you can nullify the shapechanging magic entirely, causing it to fail against the triggering target.

The grimoire has a 50% chance of actually being a mimic.  Casting the identify spell on the grimoire reveals if it is a mimic or not.  If the grimoire is revealed to be a mimic, how the mimic reacts to being discovered is up to the DM.

Grimoire Mimic

Tiny monstrosity (shapechanger), neutral

Armor Class 12 (Natural Armor)
Hit Points 7 (3d4)
Speed 20 ft.

Skills Arcana +4, Stealth +4

Damage Immunities acid

Condition Immunities prone

Senses darkvision 60 ft., passive Perception 10

Languages Understands Common And Undercommon But Can't Speak

Challenge 1/8 (25 XP)

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 can cast any 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.

Actions

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.

Notes: wizard