Domain of Fear, Magmas Shield

So I came across this youtube video

http://www.youtube.com/watch?v=Gz343OeZOW4

It is the popular 55 N/Mo build for farming a chest i believe in the DoF. I was just curious why you need a 55 Necro to do this. I don't have a Necro through NF so I just tried running to the spot with my Warrior, it was really easy but out of the 20 times , no chest.

Was just wondering if anyone knew why you cant just do heroes/hench for the chest or just run there.

Thanks for any help, its greatly apprecaited.

"The titans themselves are also known to drop the shields"

yes i saw that but if the chest doesnt spawn after 20 runs kind of ridiculous i guess, must be why the shield is pretty expesnive =P. its probably a really rare drop off those titans?

kill the titans and each group of titans that spawn (last spawn includes the rotting titan) might pop a chest with it...55s work well to wipe out the groups but h/h is fine, too