Aegis Grimoire (Patreon)

Armor (shield), very rare (requires attunement by a wizard)

This leather shield looks like a leather-bound book with brass fixtures. You're considered proficient with this shield while you're attuned to it. The shield has 5 charges and regains 1d4 + 1 expended charges daily at dawn.

Spells. While holding this shield, you can use a bonus action to expend 1 or more of its charges to cast one of the following spells from it: antilife shell (4 charges), mage armor (1 charge), or protection from energy (2 charges). When you cast this version of mage armor on yourself, it also reduces the damage you take from spells by half.

Spell Absorb. While holding this shield, you can use a reaction when you make a saving throw against a spell cast by a hostile creature to expend any number of charges from the shield. For each expended charge, you gain a +2 bonus to the saving throw. You can decide to use this reaction after making the saving throw, but before the GM says whether the roll succeeds or fails. If the number of expended charges was greater than or equal to the level of the spell, you automatically succeed on the saving throw, and the shield's cover flings itself open to reveal the large pages behind it. When this happens, the spell is inscribed in the shield's pages using a magical cipher that can't be understood or transcribed, and the cover slams back shut. The spell remains inscribed until you finish a long rest, until you inscribe a different spell with this property, or until you cast the spell from the shield using its normal casting time (no charges required); the cover flings itself back open when the spell is cast from the shield, and the paper becomes blank once more. Otherwise, the book remains closed and can't be opened. The spell is cast from the shield at the same level in which it was originally cast, and it uses your spell save DC, spell attack bonus, and spellcasting ability modifier.

"Oh, that's a fun spell. Let me give it a shot."