End Crystal

An Ender Crystal is an entity found in The End. They are found atop the many Obsidian Pillars found across The End, and their primary purpose is to recharge the health of the Ender Dragon, who will charge from the nearest Crystal within a small radius. The Ender Crystal can be placed in the world by typing /summon EnderCrystal into the command screen for Minecraft 1.7.2+.

When hit by the player, they will explode, leaving only bedrock and the pillar. The base appears to be made of Bedrock, with a crystal hovering over it and fire engulfing it. The player must destroy a majority of these in the immediate area in order to defeat the Ender Dragon effectively. If you destroy an Ender Crystal while the Ender Dragon is recharging from it, the dragon will take a small amount of damage.

The Ender Crystal's explosion is 50% more powerful than TNT, so this can easily be fatal. No wall can stop an Ender Crystal explosion reaching another crystal in range, and a chain reaction of Ender Crystal explosions is instantaneous.

Due to the fact that Ender Crystals have no clipping (can be walked through without effect), more than one can be placed on a single spot. If several exist at the exactly same location, and one of them is triggered to explode (e.g. through a snowball), the others remain unharmed.

Strategy
The most recommended method of destroying an Ender Crystal is to shoot it with an arrow, although a snowball, an egg, and even a fishing rod will work, as they are destroyed when hit by any projectile, even ones that do no damage. The exceptions to this being a Splash Potion and a Bottle o' Enchanting. The player may also climb the pillar and attempt to destroy one by hand or with a sword, but the resulting explosion will hurt the player, and likely throw them off the pillar. Also, while the player climbs the pillar, there is a risk of getting knocked off by the dragon. In order to climb a pillar, players are advised to mine the End Stone around the tower, or possibly Obsidian to build the stairs, since the ender dragon cannot remove either of those materials, instead of creating ladder or stairs out of material that might be vaporized by the Ender Dragon's touch.

Another way to reach the top of the towers is to teleport to the top with an Ender Pearl, as these are plentiful in the End.

The most time consuming way up is to use a diamond pickaxe to carve a spiral staircase inside the pillar.

Technical information
Ender Crystals have a complex appearance: A bedrock slab, fire, then three rotating cubes:  Two resembling purplish glass blocks, and one magenta block with red runes. The Ender Crystal entity "proper", consists of the wide bedrock-textured slab on and the rotating cubes. The bedrock in the middle is an actual bedrock block which the world generator places in the same location as the entity, and the fire is an actual fire block which is continuously maintained by the Ender Crystal (as bedrock does not ordinarily remain on fire EDIT: As of release 1.2.5, Bedrock in the End will burn forever if set on fire, similar to Netherrack. It can still be put out by the same methods, as well.). The healing beam appears to be an octagon.

If there is no solid block below or flammable block adjacent to the fire location, then the fire will not show up, but the crystal's attempts to do so will create flashes of light in the area, and any flammable blocks nearby will catch fire. These lighting updates may be responsible for lag noticeable when an Ender Crystal is created outside of its normal position.

The Ender Crystal entity is not solid and can be walked through freely. An Ender Dragon will pass through the crystal with impunity.

The healing beam is neither obstructed nor is it diminished by entities or blocks.

Ender Crystals can be pushed by pistons, but doing so in order to align them with a block causes them to explode. If they do not explode, they will be set on fire, to no effect.

Trivia

 * Placing water above one using a Bucket will cause a looping effect, where the fire is continuously put out and reinitialized as the water attempts to flow down and is stopped. The water will not spread, as it can flow downward, but is prevented by the reoccurring fire instantly taking its place.
 * Despite having only 1 health, Ender Crystals do not appear to be damaged by fire.
 * An exploding firework does not affect nearby ender crystals.
 * Ender Crystals can be pushed with a piston, except when pushed into a burning block, which causes it to explode.
 * Oftentimes, the fire will stay after an Ender Crystal blows up.
 * The Bedrock base will remain with the default texture for it if you are in a texture pack.
 * Very rarely, a Crystal will spawn on top of the bedrock, rather than with the bedrock inside it (see image below for clarification).
 * An Ender Crystal can heal multiple Ender Dragons at the same time.

Gallery
Enderkristall Cristal d'ender Kryształ Kresu Кристалл Края 末影水晶