Is there an boss in minecraft in nether portal?

Answer 1

Yes, as of minecraft 1.4, the Wither was added to Minecraft. It is created by placing two blocks high of soul sand, then adding two "arms" of soul sand. Then, on the three top blocks, place three Wither Skeleton Skulls, which are obtained from fighting Wither Skeletons as a rare drop, which are found in Nether Fortresses.

When you build the wither boss, it should look like this:

[SKULL] [SKULL] [SKULL]

[S . S .] [S . S .] [S . S .]

_______[S . S .]

'S . S .' stands for Soul Sand. When you build it, the wither boss will automatically spawn. I would advise building it in the Overworld, because there you will have a smaller chance of being thrown in lava.