Well, hello. I saw and read all the thread from a Google search and I would like to add my own opinion to Maryann subject and if possible to Russell too.
Many of you still haven't realized, or need, specific proof with spoken words that Maryann was an immortal being. First of all we can all agree she was a supernatural. This is too obvious, seeing her bizarre otherworldly powers that no other being in the show ever depicted.
But as a supernatural was she immortal? I put my hand on fire that in True Blood-verse Maryann, was 100% immortal. I don't know how much of an immortal she was. Vampires are immortal but if staked they die. Their weakness is fire, the stake and BOOM. True Death.
As Sophie Ann stated, a maenad's True Death is to succumb to her god. To drop down her immortality shield and totally give in. I don't know why but Sophie Ann seemed pretty sure of what she was talking about.
The show MANY TIMES, even though never truly revealed what powers Maryann had, showed that at a limited scope she COULD kill with bare hands and she could defeat any supernatural. It was never shown but the way the actress (michelle forbes) treated the role, showed a cool way to grab sookie's neck with ease. The speed was also a thing but sometimes I wonder why didn't she run fast to catch up with Sam or why she couldn't hypnotize other supes.
Let's also mention the komodo poison from her nails, it could actually HURT other supes and kill them, when she actually transformed to half bull. She also depicted some kind of aerokinetic abilites, a kind of screech like a flock of birds, that power maybe was the source of her normal vibrating power because it too, didn't affect other supes but only humans and it seemed to be capable to kill them.
Now, the deflecting bullet debate. Sometimes I really thought what if Maryann wasn't that of a powerful immortal and could easily be decapitated or smashed to pieces by an RPG? But the scene with Lafayette shoting her made me rethink and be sure about her invicibility. Nothing can pierce her because she doesn't believe she can be pierced. It may seem vague but THIS made her immortal and it made it true. Otherwise the bullet would pierce her hand, instead it deflected like nothing. It's so obvious, they put it there for a reason.
A friend of mine insisted that she deflected it because she defenced herself. Why defend herself if the bullet can't smash her head in two? Maybe it was a cool thing to show on television, to deflect a bullet and show her invincible powers, rather than depicting her gleeful being hit at the head and laughing. But I'm sure she was proof from damage.
I won't take it far or mention other possibilities like burning her, throwing her over a precipice or smashing her with something, I really don't know. She probably wouldn't let someone to do it. One of the few proofs that she was exceptionally powerful was her age. Over 10000 years old, her side kick Daphne stated she was always there and people feared her in ancient times calling her Lilith or Gaea, primeval deities.
Ugh it's so obvious already. Maryann was like devil, much older than vampires and it was subtly revealed to us all that she lived in primitive eras of sacrifices and the first cavemen. Maybe she was much older. She also probably came from ancient cults of orphism and she was a mystic in rituals (based on the greek words i heard and know what mean while sookie overheard her thoughts). Her mythology in general reveals a lot about her identity as an ancient being of reincarnation, half bird half human and believe me. It has nothing to do with weak characters or mortals cloacked in words of immortality but real gods and demons.
Sorry for the long post but some people really disregarded her and went to deify Russell. I like Russell too, A LOT. BUT sometimes outright strength is not the only thing that can beat. As Alan Ball said, for characters' luck Maryann's dead. She was the most powerful character of both the show and the books. In the books she was unkillable as the author stated.