The Crystal Shield is a mid-to-high-ranked shield in Final Fantasy XII that boosts the wearer's physical evade by 23 and their Magick Evade by 10. It is likely the first shield the player comes across provides any Magick Evade, and thus eclipses the shields they had before, besides for elemental resistances for for the Shell Shield's Auto-Shell.
In the original PlayStation 2 version, the Crystal Shield is bought for 7,200 gil from Archades and Balfonheim Port. It is also found in a treasure in Pharos - First Ascent's Wellspring Labyrinth (north; 65% chance to appear, 25% chance for gil, 50% chance the item treasure is Crystal Shield without the Diamond Armlet equipped ). The Crystal Shield is the reward for the hunt for Vyraal.
In the updated Zodiac versions, the Crystal Shield can be bought for 6,360 gil in Phon Coast and Archades. It is found in a treasure in Phon Coast's Cape Tialan (70% chance to appear, 50% chance for gil, 50% chance the item treasure is Crystal Shield without the Diamond Armlet equipped) and Tchita Uplands' Sundered Earth (30% chance to appear, 70% chance for gil, 50% chance the item treasure is Crystal Shield without the Diamond Armlet equipped).
The Crystal Shield is a mid-to-high-ranked shield that helps the wielder evade both physical and magickal attacks, making it better than most other shields when equipped to provide evasion over any other effect they may bestow. However, at this point in the game, two-handed weapons tend to be superior to one-handed ones, and most times it is not worthwhile to sacrifice the increased damage from a two-handed weapon to be able to equip a shield. In the Zodiac versions, the Crystal Shield can be used by the jobs Red Battlemage, Knight, Foebreaker and Shikari. Out of these, Foebreaker with their axes and hammers can keep equipping shields until endgame, but in The Zodiac Age each character can unlock two License Boards, and so the Foebreaker may also have access to a better two-handed weapon by this point.
The Crystal Shield can be equipped by characters with one-handed weapons or no weapon in their available hand. It adds to the wearer's physical and magickal evasion. Shield Block augments also add +5% to both physical and magickal evasion per augment purchased. Magick evasion does not block status effect spells (the player needs to use Shell to halve their chance unless they can get immunity from equipment). Equipping a shield negates the Brawler augment, even if the character is still attacking bare-handed. Some enemies, especially all the toughest bosses and marks, have Ignore Evasion as a passive ability, which causes their attacks to ignore all blocking and parrying.
The chance to block granted by gloves and shields and Shield Block licenses is checked separately to, and before, the evade from one-handed weapons. If the shield block fails, the game checks for the weapon block, and if that fails, the game checks for parry.