The orc boss appears after lvl 10 - it's just you and him in a confined area.
He has a pattern:
As he comes toward you run at him and jump over him.
He will then start whacking his sword.
Get about 5-6 swipes on him from behind, you don't need to be very close to him to do dmg.
Now back away because he's about to throw a spear which comes at you quickly.
Jump over the spear.
} Until (Dead)