Low Level Duelers

Ive always liked those level 20s kicking a level 40+ arse when i play in a blood run game. I was wondering what and how to make these low level duelers.....

I was playing the other day and saw a level 20 barb (throwing barb) just kill 5 people who challenged him all above level 35....
and twice kill a level 70+ player.....

I have also seen other low level chars do this but probably i think the barb or the paladin would be more efficient killers....

Can somone suggest on how to make these low level duelers and what points and skills must be put in and also equipment advice.....THNX