Duriel once was hard
hi.
you do not need a Valk or a Act2 merc to defeat Duriel.
what you need to defeat Duriel is the skill 'SlowMonsters'. a perfect and easy to find item is 'Clegs Pincers'. use the fastest boots you can find, try for 30% or higher.
before you enter Duriels tomb, drink lots of 'thawing potions', have a tp scroll in your belt. when entering the tomb immediately cast the tp.
if Duriel homes in on you, then run in circular pattern around the tomb, keep turning and fireing at him, he will not be able to get to you because of the 'SlowMonsters'.
hopefuly Duriel will have attacked your merc, if so, then fire away at him, making sure you keep your mercs health high.
if you need to escape the tomb, then use the tp you have already cast. upon reentering the tomb, make sure you have placed another tp scroll in your belt and cast this as soon as you reenter.
Duriel, like all Bosses are Demons. so any item that give 'enhanced damage to demons' is a must for a amazon.