Which one is correct and why?

It depends. You might mean the archaic "would". What is the context?

The context is given right above. Would in the context is past of Will

I have said no dreamwalker will come here. Correct.. No dreamwalker will ever show up here.
I have said no dreamwalker would come here Correct. No dreamwalker wants to come here. This place is not desirable to them.

AnonymousThe context is given right above. Would in the context is past of Will

http://www.merriam-webster.com/dictionary/context

There's also simple back shifting.

Yesterday and the day before and the week before, I said "No dreamwalker will come."
I have said that no dreamwalker would come. -- A correct way to back shift "will" to "would" in reported speech.
I have said that no dreamwalker will come. -- A correct way to show reported speech when the thing talked about is still true.

I find "will"

Ok thanks for your reply, I want to ask a further question, if I use in the context past simple instead of present perfect, in this case whick one should be correct:
I said no dreamwalker will come here or I said no dreamwalker would come here

AnonymousOk thanks for your reply, I want to ask a further question, if I use in the context past simple instead of present perfect, in this case whick one should be correct:

The answers would be the same.