These seem to be called "Graven Mage Schools" according to the Graven Mage School talisman.

Looks like the Abhorrent Flesh and Frozen Flesh (balls with spikes, made of Lost heads) in Code Vein. I wonder which was the original inspiration.

So, as far as I can tell, these are actually amalgamations of mages that practiced primeval sorcery. Every reference we have seen in the game so far to primal, primeval, etc has all related to the crucible, which is a time before everything when all life was combined into one thing. If you follow Sellen's Questline, (SPOILERS) at the very end, the two banished archmages of the Raya Lucaria Academy will disappear, and Sellen will now be turned into one of these schools of mages. Graven just means to be cast into stone, AKA engraved. So if they are a school of mages (like a school of fish, but since mages are students, they are a school of mages, engraved into stone. As in the mages themselves have been turned into a single stone orb. It is my understanding by reading the item descriptions that this is the destiny of any sorcerer studying primeval current sorcery. I think the point of that sorcery is to recombine everything back into one, like with the crucible. I think that sellen combined herself with the two archmages and became the school of graven mages you find in the academy who is called Sellen. Also, you will find these creatures all over the lands between, and in the descriptions in the talismans it calls them the great mistake of the academy. As in the mages started to practice this, and it scared the academy so much, that they banished anybody who practiced it, all the way to the top.

Apparently these "Graven Masses" are the result of Sorcerers who tried to combine the power of their Primal Glintstone with others. What greed does to a mf.

There’s also one behind the Ainsel River Well in Liurnia

I'm not convinced that these things were once sorcerers. Per the description, they are meant for guarding important magic. Each of the ones found in the game is acting in this capacity. With Sellen, my belief is that she attempted rebirth while in her puppet body, which triggered a trap laid by Seluvis. There is a note in his lab warning against touching his stuff, after all.

Reminds me of natural caused phenomena "rat king", when many rats are tied together with their tails, it forms a grotesque rodent mass.

There is ONE ANOTHER right above Ainsel River Well where bear is also comes the Sphere from the small Pond Seems missing in here

Sacred blade ashes helps with killing it alot and it drops around 900 runes when killed. Just wait till it stops spewing the blue and run in to hit it as it goes back down to the ground. Avoid the spray but it seems to have a pattern to the spray directions

Everybody gangsta till big *** ball with rock candy eyes shows up and starts shooting mortar like lasers