Looks like all the info from Doctorugh's edit is correct (Unsure about resistance being light based):
Code:
HP Target DMG rHP Weapon?
1580 Yag BLM 69 35% O
1580 Mandy 171 18% O
1580 Bee 145 18% O
1580 Yag SAM 155 35% O
1580 Dhalmel 200 35% O
1580 Bee 153 18% O
1580 Sapling 136 35% O
1580 Weapon 256 35% O
1580 Pixie 135 35% O
1580 Weapon (Xarc) 487 75% X
1580 Weapon(Xarc) 553 71% X
1580 Weapon(Xarc) 1305 35% O
1580 Weapon(Xarc) 1305 35% O
1580 Weapon(Xarc) 1200 35% X
1580 Elemental 131 91% O
1580 Skeleton 560 69% O
1580 Skeleton 434 76% O
1580 Skeleton 379 80% O
1580 Skeleton (KRT) 24 68% O
1580 Skeleton(KRT) 34 68% O
Critical HP Goblin 12 89% O
Critical HP Goblin 42 71% O
1580 Marid NM 235 99% X
Critical HP Marid NM 0 100% O
Critical HP Djinn 7 99% X
500 Chigoe 630 39% O
600 Chigoe 336 68% O
600 Chigoe 342 66% O
1505 Sapling 1269 60% O
601 Chigoe 702 35% O
At slightly less than 50% of the mob's HP (Chigoes have ~1.1k HP), you get the mob to 39% HP (Cannot be half resist). At 600 HP (Over half their HP) I was able to land full damage with ES. Without ES, I managed to land a half resist.
I'm going to contest the light based resistance though because I was able to bring a light elemental (Sky) to roughly 85% HP. I only managed ~90% HP on a ice elemental at Xarcabard and 90% on a water elemental at Cae Mire. Remember that this is considered a piercing damage physical spell, so elemental's physical resistance explains the reduced damage. Could use extra testing, but sick of this atm.
Edit: Interesting question though! We see that the NM took 0DMG from the NM. If that is due to PDT, this spell may be useful for tracking whether a mob has PDT or just high DEF.