The Shell Shield is a shield in Final Fantasy XII that slightly boosts the wearer's physical evade and gives them a constant Shell effect, reducing magickal damage to the wearer by 33% and halving the success rate of status ailments, including instant death, which can't otherwise be protected against. It is metallic for the purposes of the magnetize debuff present in the Vinuskar and Ultima boss battles.
Despite being a shield focused on magickal defense, it does not provide any magick evasion, although the Shell halving status spells' accuracy is similar. Due to this property, Shell Shield remains useful equipment to situationally wear until the end of game, even against enemies that ignore evade.
In the original PlayStation 2 version, the Shell Shield can't be bought in shops but sells for 7,500 gil. It is found in a treasure in Stilshrine of Miriam's Cold Distance (see below), Tchita Uplands' The Highlands (in the west part of the area, a bit south of some ruins; 10% chance to appear, 50% chance for gil, 50% chance the item treasure is a Shell Shield without the Diamond Armlet equipped ), and Cerobi Steppe's The Terraced Bank (50% chance to appear, 50% chance for gil, 10% chance the item treasure is a Shell Shield with the Diamond Armlet equipped ).
To get the shield at the Stilshrine of Miriam the player must locate a hidden passage. In the Ward of the Sword-King there is a junction: the path to the left has a wall that will vanish if the player approaches it in a way the camera will attempt to go "inside" the wall. At the end of the path is a treasure that never respawns that has either a Dark Matter or a Shell Shield. With the Diamond Armlet equipped, the treasure is 90% Shell Shield, 10% Dark Matter. When entering the last room after the hidden passage the player should cast Float before entering, because the entrance is covered in traps.
In the updated Zodiac versions, the Shell Shield can't be bought from shops but sells for 5,000 gil. It is still a treasure in the Stilshrine of Miriam's Cold Distance, now as a guaranteed treasure, and newly in Cerobi Steppe's The Northsward (20% chance to appear, 80% chance for gil, 5% chance the item treasure is a Shell Shield with the Diamond Armlet equipped).
It is still the reward for the hunt for the Wyvern Lord.
The Shell Shield is a shield with great utility more so for the Shell buff than for its ability to evade physical attacks. In the Zodiac versions, it can be used by the jobs Red Battlemage, Knight, and Foebreaker. A constant Shell effect is useful against enemies that use magick, and it can be especially useful in the superboss battles against Yiazmat and Zodiark for its ability to reduce the chance of instant death hitting, a status not normally protected against by any means. In these battles the player may want to use a dedicated healer or mage character, who could then just wield the shield and forgo wearing a weapon, if needed, as magick can be used fine without one. However, in The Zodiac Age versions, any mage/healing class would need to be paired with a job that can equip the Shell Shield, and in the base Zodiac Job System version, only one License Board is available per character.
An alternative would be to set up a Self:Shell gambit. With Shellga the player can protect the whole party at once, but as status duration depends on Vitality, it might expire at different rates on different party members, and thus automating it with gambits can still take a lot of time. The big benefit of Shell Shield is that the character can be revived with Shell status already in place. Another magick-focused shield is the late game Aegis Shield that provides 50 Magick Evade.
The Shell Shield can be equipped by characters with one-handed weapons or no weapon in their available hand. It adds to the wearer's physical evasion. Shield Block augments also add +5% to physical evasion per augment purchased. 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.