Use one of the following entries with the mm_npc_create code.

Arantir
aratrok
cyclope
death_knight_sword
death_knight_sword_shield
ghoul
goblin
human_guard
human_guard_bow
Leanna
lich
Menelag
necromancer
orc_sword
orc_sword_bow
orc_sword_shield
Phenrig
undead
villager_undead