Rank 40 seems to give enemies max HP when they get stoned when it states the bearer is suppose to. It also only procs when the bearer is the one to inflict stone, and not just in general.
Aside from that, it’s rank 80 is confusing. It states it ignores enemies resistances to stone, yet enemies still get the icon for it’s resistance. Not sure if it’s just bypassing it in the background even though the resistance icon is still there.