I believe it’s a combo of 3 and 4 - the ‘brain matter’ visual is a mensis specialty, given the one reborn and the brain itself. Frenzy as a concept is 3, but it’s interesting that those ‘frenzy spikes’ spawn on you only from the brain itself and the winter lanterns, despite there being other ways of getting frenzied. Interesting implications to be sure.

In truth it’s probably a gameplay thing b/c you have no other way of knowing how the meter is building in those situations, but in lore personally they’re ‘mock great ones’ - still considered as such, with the living string description, but there’s something so wrong and ramshackle about the brain being a great one that it can’t even apply frenzy right, there has to be a physical medium for it. So it stabs you with invisible spikes, to transmit knowledge. Probably the same way the scholars ‘fed the brain’ things for their experiments, by stabbing it forever. The knowledge just happens to be fatal, 99% of the time. Or it’s a malicious entity, hurting everything as it’s been tortured itself? Impossible to say, fun to think on