From Fallen London Wiki

If this truly a new attribute, then we can make it MAGICCATSZ, which is just delightful.

I'm being a little skeptical, though, due to *extremely* nitpicky reading of the action that grants the item.

It is Dangerous, grants Inerrant, and raises Kataleptic Toxicology.

Note how it uses three different verbs for the stats. Generally items are shadowy, or bizarre. And they usually grant or raise zeefaring. It's a bit odd this would grant Inerrant but raise KT, which makes me suspect it might be a boolean attribute rather than a numeric stat. But, who knows, I could be jumping at shadows and it wouldn't be the first time.

I do hope it's a new general stat. I would be slightly disappointed if the culmination of beating HG is getting an attribute that only affects HG.