Yes, but the enderdragon may be added in later versions of each version of the game
The Ender Dragon and the Wither are currently the only boss monsters in minecraft.
There is not an End Castle in minecraft, the End is basically only to fight the Ender Dragon. But maybe we will see a Ender Castle in further updates.
No, creeper dragons do not yet exist in Minecraft. The only type of dragon that currently exists is the Enderdragon.
No however in a new update it may be possible. The only rideable mob in minecraft is a pig.
A standard stack in Minecraft is 64. However, certain items, including ender pearls and snowballs can only be stacked to 16.
The wither has 300 hearts however the ender dragon can regen health but only has 200 hearts.
Ender Portals are unbuildable in Singleplayer, but if you go into creative mode, you'll find the End Portal Frames and Ender Eyes in one of the tabs, the only way to find them in Singleplayer survival is to use Ender Eyes to follow and find the location of the Strongholds of the Portals.
no only gameboy advance
Minecraft is all about the account you made, you can log into that account on any computer, you are not forced to play it only on the computer that you purchased it on.
Like a locked chest that only you can access? You can't. You can, however, make an Ender Chest, which is basically a global chest that you can access from any Ender Chest. Only you can access your own Ender Chest inventory.
No. There is only the ender dragon. However, if you have the 1.4.2 update, there is a new boss called the Wither. i'm not sure what it is yet though.
No. The latest update only has the nether reactor, which technically doesn't teleport to another world. We can only hope for an update for the end.