Creating your own hero.

Froska, first, I want to change the picture, name, and biography. Second... well... probably a Necromancer. What exactly do you need?

And can I create my own specialization? (i.e., my own drawing and my own property)

It would be more helpful if you were more specific...
Otherwise, you just need to choose a Necromancer hero with the specialization you need. Then, use the spacebar to bring up the properties. You can upload an icon, but I'm not sure if the editor will understand it, as I haven't done that. Then, change all the properties to your own.
It's very easy to figure out. ;)

Creating your own specializations is practically impossible for ordinary users at the moment. You can create a primitive one with scripts, but the scripts are not very easy to understand. So, it's better to stick to the existing ones.