Pet Food Alpha describes the process of working through these new monsters. There are 31 in all, each at a specific tier of content. The tiers have to be climbed in order to reach the most dangerous creatures, with a single fifth-tier monster called Pandemonium Warden being the ultimate goal. A collaboration of linkshells (guilds) worked day and night all month to reach the point where they could take on this beast ... only to have a low level 'test goblin' spawn in place of the monsterous ZNM finale. The developers are on the case.
For more on this new system, check out the hugely informative Blue Gartr discussion thread on the subject or check below the cut to watch a 1st tier ZNM fight with the creature Ob.