First Group of Ideas
Maybe when they are lying down and resting, the will curl around the bottom of the gem tree of its gem tree island where it spawned (one for every gem tree island) with a rather nice little animation when it lies down to sleep. If a player comes within 20 blocks in any direction, it will wake up and start flying in a circle around the tree until the player comes ten blocks within range. It will start attacking if the player does not leave to 15 blocks or more away from it in 4 seconds. It will play sounds for the going-to-sleep animation, the waking animation, for flying, and for attacking.
The Type of Dragon
Another factor that plays in the size of the dragon, the damage it can deal, and the color (including the fire’s color) also varies according to the kind of tree* it spawns of. For example, a ruby dragon would be larger than an amethyst dragon, deal more damage, and have red fire (the fire would be of more reddish color than of regular color of fire. The color of the fire would effect the color of the fire on a block. If another dragon of another color lights the same blocks, it will not mix. The second dragon’s fire will be shown instead). Killing the dragon will provide you either five diamonds, seven rubies, &c., adding two for every lower level. If shot with a bow from eleven blocks away or further, they will immediately start attacking, even though you are not within range, or else that would be totally not right, because it would be too easy. They will rest at midday and at night.
At the Stroke of Twelve
At midnight they awake, with every one of their positive attributes doubled (e.g. the detection range will be forty instead of twenty), and glowing brightly, somewhat like a chandelier. At this time, if they are killed, they will give twice as many gems.
Two in-game days after they are killed, an animation will play (I haven’t come up with it yet), showing a new baby dragon.
They can also respawn by reproducing. If the dragon nears the end of its life, it will lay an egg that requires five days to hatch. The dragon cannot be respawned if its tree is cut down. See below
The dragons cannot survive if their tree is cut down. The dragon can be immediately killed by doing this, and will not respawn if this is done. Coming within three blocks near the tree will provoke the dragon, doubling the damage it can deal (yeah… Midnight can be really dangerous at this point See two above).
Taming (I came up with this because of the comment by @kaypoppy)
By feeding the dragon it corresponding gem, you can tame it. The amount of gems needed varies, although the range increases for the higher level of dragon, the minimum added by one for every level, and the maximum by two. For example, the minimum of an amethyst dragon is five, it’s maximum being ten, whereas a sapphire’s minimum is six, and its maximum is twelve. I would think you would ride on the dragons neck (the four lower levels can only have one passenger, but the diamond’s bonus is two passengers. The tamer is the only one who can ride them, but after the tamer is upon the diamond, somebody else can get on the back. A dragon saddle is required for the tamer to ride, but a dragon chair is required for the passenger. The dragon will act mostly like the jetpack, although when you attack somebody, the dragon can attack. Wild dragons have 500 hp, tamed have 700 hp. After taming a dragon, it will show up as a blockhead on your screen, although it cannot be controlled like one. If you have your blockhead as the dragon, there will be no inventory, but there is a “Call dragon” button. If pressed, you only have to tap on the blockhead that you want it to report to (from its screen). A tamed dragon has no life force. After tamed, its spawn island will recognize the dragon as killed, and start the spawn process, taking only one day though, to make another dragon. If riding the dragon and you come within the detection range of the same type of dragon, it will not attack. If you dismount and the tamed dragon leaves the detection range of the aforementioned** dragon, it will attack.
*Shariu’s idea for the dragon’s color.
**Sorry if I bored you with this word.
Not all of these ideas need to be included.
(You also don’t have to read the entire comment, including this sentence)
Note: tamed dragons do not retain the midnight thingy.