Crystal ward

The Crystal shield is a powerful shield available after a player completes the Roving Elves quest, and a possible reward from this quest along with the Crystal Bow. To wield the crystal shield, a player must have 70 Defence and 50 Agility. It can be considered similar to the Barrows rewards due to its substantial power and pricy repair costs. The Crystal shield is especially good against Ranged attacks and is in fact the strongest non-dungeoneering shield against ranged attacks, while at full charge. It also holds the strongest defence against Summoning familiar's attacks.

The crystal shield degrades over time. When a player obtains a new crystal shield, it will be a "New crystal shield". However, after 2500 hits, it degrades into a "Crystal shield 9/10", and for every 2500 hits taken thereafter it will degrade another 1/10th, until it reverts into a crystal seed after a total of 25,000 hits taken. As the crystal shield degrades, its defence bonus drops. Once the crystal shield has reverted to a crystal seed, a player can buy a new crystal shield for the cost of 750,000 coins, or have their crystal seed enchanted into a shield by Ilfeen. When you get a crystal shield recharged, it will become untradeable. While having the seed re-enchanted costs 750,000 coins for the first time, the price lowers each time you get it re-enchanted. The first recharge costs 750k coins, the second 600k coins, the third 450k coins, the fourth 300k coins, and the fifth and every time thereafter costs 150k. It is important to note that the count of the number of times you have had an object recharged is shared between the crystal bow and shield. If you have had a crystal bow recharged twice, then a shield recharge would cost 450k, as if you had already recharged it twice as well.

It should be noted that this shield's bonuses are similar to those of the dragon sq shield, which is cheaper and does not degrade.

Bonuses over course of degradation
As the shield degrades the negative magic and range attack bonuses remain the same while the positive bonuses decrease as shown below.

Rapid degrading
An interesting thing to note is that if you are pickpocketing somebody and happen to fail, the amount they hit you for also counts against your shield's charges. Thus, pickpocketing is an effective way to degrade your crystal shield. The quickest way to degrade the crystal shield is to go into any dungeon that requires a light source with only food in your inventory and the shield equipped. All of the insect damage will count against your shield's charges. Players will often use the shortcut between Lumbridge Castle Basement and the Dorgeshuun mine for this purpose, since the area is both close to a bank and a respawn point.

Another effective way to degrade your Crystal Shield is (If you have completed the Creature Of Fenkenstrain quest) to go into the cave of experiments (take only your crystal shield), and hit one, Then click a nearby square to stop attacking it (Make sure you have auto-retaliate off). Since Experiments do not hit often at all you will take little or no damage every time it hits you. This is a great way to degrade your crystal shield. Those with access to Oo'glog's pools can boost their lifepoints, run out to fight several ogress warriors and return to the pool occasionally for a cheap but fast way to degrade the shield. The fastest way to degrade the shield is by going into the Lumbridge cellar dungeon after the Lost Tribe quest without a lantern. You will lose all of your Lifepoints in seconds. Also, if your spawn point is in Lumbridge, you can degrade the shield in less than 10 minutes, depending on your constitution level.

You may also choose to degrade your shield via the player-built flame pit in the Oubliette. These flames hit extremely fast and deal low damage per hit - also, upon death, all of your items will be kept and you will appear outside the house portal, making this a fast and safe way to degrade your shield. You can use another person's house, so you do not need to own a flame pit. Building a flame pit will cost 125,000 coins as well as 20 tinderboxes, requiring 77 construction and granting 357 experience.

Trivia

 * Even though it takes only 50 Agility to wield the crystal shield, an agility level of 56 (although temporary boosts may be used) is needed to complete the Regicide quest, which is a prerequisite to complete the Roving Elves quest. It is however, possible to buy the shield from the Grand Exchange at full charge, but it cannot be wielded until Roving Elves is complete.
 * If a player attempts to cast low level alchemy or high level alchemy on a Crystal shield, they will receive a message saying 'You can't do that to elven crystal!' because of a bug allowing you to alch recharged crystal armour and weapons in f2p worlds for 900k.
 * One could pay less for a crystal shield by degrading the partially damaged one you receive from the end of Roving Elves, selling the crystal seed on the Grand Exchange, and then buying a brand new shield from Islwyn with some of the money you received from the seed, thus saving about 200K. You are saving money because to recharge a crystal shield costs 750K, and you also must have a seed with you already. However this is a short-sighted strategy, since the cost of recharging the shield falls rapidly, whereas the cost of a new one stays the same.
 * The shield resembles the head of a Venus flytrap.
 * The Crystal Shield has one of the highest damage absorption rates out of all the shields.