User blog comment:Blademaster00/Official Amatsumagatsuchi Talk Page/@comment-86.18.80.90-20101201201502/@comment-969093-20101201211828

Depends on what you consider as "difficult". In terms of sheer power not a single monster in the 3rd generation was actually able to instant-kill a hunter. :/ From the looks of it it would likely be a Giant-Monster type of battle such as Lao/Shen/Ceadeus/Jhen. He'd have more HP, definitely, but power-wise he'll probably no different from those 4.