Got this from the Demi-Human Queen(?) in the Demi-Human Ruins in Limgrave.

Weak damage, low range (sawed-off shotgun style). Does significant stagger damage close range vs big enemies , especially if charged. Can hit weakspots like heads on giants, managed to knock down one of them in ~3 good hits, 2 if charged headshots connected. Mediocre outside of surprising CC potential.

hopefully fromsoft hotfixes sorcery. Glintstone pebble seems to be the strongest spell in the game.

Bad range, poor damage.
It might be useful if charged, but you can't charge it while enemies are close enough for the spell to actually hit, or they'll just come up and smack you.

Literally a meme spell

Quite underwhelming spell.
When charged it deals somewhat more damage than glintstone pebble, lower otherwise. It however requires you to be in close range or you risk that not all shards connect with the enemy thus lowering your damage. And this costs twice as much FP as a single pebble.

It seems it's good for staggering enemies though, but it's a high commitment spell given it's poor range.

So bad not even the caveman mini-boss that uses it can't hit you with it.

Is it supposed to be guaranteed or just a chance that it drops? Because I keep killing her and she hasn't dropped the spell or the staff.

At 85 INT with +9 Lusat staff I 2-shot the giant outside the Godrick boss fight. Huge damage for such a low fp sorcery but you have to be VERY close to make it worth using and as a glass cannon caster you usually don't want that lol Use it to cheese bigger enemies but i'd suggest avoiding it otherwise. Same goes for PVP, have one-shot several players with this but have been one-shot myself just as often :)