Depending on what zone it was in or what rare boss it was.. I think being a rare boss mob spawn would be awesome.. I would just /Emote random things like fits of maniacal laughter, or berating a minion.. and shout to the zone about how my experiment failed and I needed more subjects, or that my last minion was a worthless, but delicious.. OR! Lure adventurers to me with false pleas of help, acting a damsel in distress and then charming the characters that come to my aid.
A guard most definitely; kill stealing newbies' bats, rats, snakes- and decaying skeltons with cracked staves!