i am not talking about this vader tryout in certain, it was rather a general question and the vader was the example.

no offense but you are really not much of a help, at least not more than i could figure out myself ;-)
How do you expect people to help you if you don't ask the question you actually want the answer to ?

Basically you did not have enough support.
Me I don't like support so I'd have printed it on it's head. Drop it about 0.3mm below the print bed and you'd have a nice flat spot on top of his helmet to print from.

To get better results you need to slow down your print speed - a lot !
i3's are cheap and do good prints - but they do not work fast.
try printing at 40-50mm/s. Also increase your retraction settings, both speed and length.

Drop your print temp to about 200.

link to the file on thingiverse would also help. Just because you can't get the instructions does not mean someone else can't.