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.
Chat with our AI personalities
In order to to the nether you need a portal.
Yes. There are minecraft servers that have skyblock with nether enabled that are cracked.
A Nether portal is an obsidian structure that can transport players to or from the Nether dimension. USB doesn't come into it anywhere. The 'Minecraft USB nether portal' is just a YouTube fake.
nothing :(
There is no cordinates to it,but you can find it in the Nether. That's all I know where it is.