maybe it was ninja gaiden 1 or 3 then that i couldn't beat? or maybe you guys are total badasses!

I think ninja gaiden 1 was the really hard one. If the final boss beat you, you got sent back a number of levels, I think. Number 2 was very easy.

IIRC, you can deflect the explosive knives if you block when they throw them at you. If you keep jumping that helps too. Go for the Swallow attack and you should be able to behead each one in 2 shots.