Answer these questions plz

[Feryar]

2.How can I beat Diablo at l.20-Normal,l.25-Nightmare,l.30-Hell?What are the requirements?

I'm not exactly sure what you are asking about here, but;

To make a game on Normal difficulty, you can be of any level.
To make a game on Nightmare difficulty, you are required to be level 20.
To make a game on Hell difficulty, you are required to be level 30.
Note that this is your character level, and that it only works in multiplayer. You can't make games of higher difficulty in singleplayer unless you exploit a bug that requires you to have a high level character in multiplayer. (which kind of defeats the point of playing singleplater on higher difficulty ;))

The only requirement that exists for killing Diablo at for example level 30 on hell difficulty is that you are able to do it :) Doing that is called a 3@30 and was a very popular feat (for all I know maybe it still is) back on the DSF forum. You can read about some 3@30 here: http://jc316.stormpages.com/diablo/vt3at30.html

I never tried it myself, but I'm sure beating Diablo in normal at level 20 (1@20) and nightmare at 25 (2@25) is possible as well. It all depends on how well you plan your character really.

I hope this answered your question :)