Enderdragons are in the game already, but i suggest some things changing to it.
The Enderdragon will now respawn 8 minutes after the death of the previous dragon. He will still only spawn in the End. Only the first dragon will create a portal and have the dragon egg as a block on top. Every time the dragon respawns, all pieces of bedrock exept the ones in the Overworld Portal will have a Ender Crystal spawn on them.
On death, the Enderdragon will drop 17-34 Dragon Scales and 3-8 Dragon Bones. With exeption of the first dragon, the Enderdragons will also drop a Enderdragon Egg as a item, not as a block, and will drop the regular
The Enderdragon will no longer destroy any blocks not part of the End (End Stone, Bedrock and Obsidian) but can still pass trough them. This is really useful if you're a ranger and are making a dirt tower to get to the Ender Crystals, as you'll only get knocked off and could just climb it again.
The Enderdragon won't take any damage until all Ender Crystals have been destroyed. To destroy Ender Crystals, a melee attack is required. They still only have 1 hp, so wether you're using the best possible mace ever or a sapling, it'll always die and knock you off the tower in the explosion that creates. Ender Crystals will spawn every time a Enderdragon spawns.
The Enderdragon will now sometimes come down from the sky, grab the closest player and lift him into the air, holding him for 5-10 seconds, then dropping him down. The drop can occur off the island, causing the player to fall into oblivion and die.
The Enderdragon will create a purple, pulsing light in its mouth, then shoot it at a player, wich will always do 10000 damage if it hits him. It'll slowly thrust itself forward and if it reaches a block, it'll form a black hole wich will suck players into it in a range of 25 blocks, the closer you are, the stronger the suction. If you come too close, you will take 1 dmg/0.1 second (no crits). The black hole blocks will last for 35 seconds.
Hatching the eggEdit
I also think the egg should be hatchable. For this to happen, the egg would have to be combined with a Eye of Ender in a crafting table so you could get a "Fertilized Enderdragon Egg", wich has to be put in the middle of a 3x3 obsidian box and will take 7 minecraft days to hatch. Once these have passed, the obsidian will be transformed into obsidian with little white veins going trough it. These stones can be broken with the fist, and whatever player breaks the first stone will become the owner of the dragon and can ride it using Dragon Saddles, they can't despawn and have insane regeneration (can only be slain by admins).
You must feed the Ender Dragon with one ender pearl every week. Otherwise, you will have a feral, hostile, and very mad Ender Dragon on your hands. Multiplayer has an exeption for this; see Feeding Dragons.