Gui
I feel that Abram's quest is meant to be hard so you can't use potions to so easily brute force the boss encounters. still, I can offer a couple of tips on vanquishing Mandragoras.
The first one is if you've made enough progress, you should be employing the Nitesco Glyph, which does fire and light attribute damage. if you're at the point of having Nitesco, you should also employ Rapidus Fio, which increases your movement speed in a very significant way and also makes the task of farming the roots much easier.
if you are at the point of the game where you first encounter the mandragora enemy, it would be much easier for you to employ Ignis and Sapiens Fio. I imagine ignis was easily acquired via the demons, but in the case of Sapiens fio, getting it at oblivion ridge isn't a very easy task, and requires smart use of the jump-kick that you get from the double jump. to perform a jump kick, double jump, then hold down and the direction you want to kick in while hitting the jump button. if you successfully connect with a fleaman or a albatross, you'll bounce up and be able to jump kick again, hopefully getting you up to the ledge where Sapiens Fio resides.
if you're STILL having trouble doing enough damage after raising your intelligence and shooting with Ignis, I'd also suggest trying to find the Red Drops Candy, which will raise your fire attribute by quite a bit. failing that there is a couple of good ways to grind attribute points, but I won't get into that here because I feel grinding for attribute points would be a further weaponization Gui would employ against the game.
I think you should wait to do that side quest if you're having trouble and having to spam glyph unions. Actually, Glyph Unions are the thing I have a lot of issue with in this game, as it's VERY easy to break the game by spamming them at bosses... especially after you have Vol Umbra + Vol Luminatio, Nitesco + any weapon Glyph, or Vol Grando glyph unions.