Most dark wizards as well as beings tend to have certain letters in them:
M O R:
saRuMan
sauROn
MORgoth
and of course our very favorite
vOldeMORt
These give the name a certain dark tone. So, be sure you include at least two of them. Suggestions:
Romvark the Bladderless
Mork from Ork
Vorlok of Mormon Castle
Moron the Wrong
-Doc