Generally level 30 + can take on all worlds without to much dramas (depending on your build).
As for the 4-2 boss he is a breeze.. if you got magic or a bow then you can kill him easy. He is blind so only reacts to movement. Walk slowly and he wont find you. He will however attack random places as he walks around. Attack him repeatedly and he will have an idea of where you are and do a charging attack to that location. Just roll out of the way and walk again (dont panic and run or he will kill you) as he will continue walking off somewhere and attacking random spots. So just attack him in a timely mater (i.e shoot him with arrow or magic then wait a sec or 2 then shoot again). Easiest way to kill him.