I wouldn't swear to it, but I suspect your chances at "Spell: Torpor" are something like this:
Code:
NPC ID NPC Name NPC Level Drop Chance(%) Drop Multiplier
91191 a guardian wurm 60 1.3 x 1
108512 Druushk 67 1 x 1
89144 Emperor Chottal 60 1 x 1
96089 Faydedar 55 2 x 1
86014 Gorenaire 60 4 x 1
108507 guardian wurm 61 0.1 x 1
108506 guardian wurm 60 0.1 x 1
120057 Harla Dar 66 0.5 x 1
108517 Hoshkar 66 1 x 1
87151 Ixiblat Fer 62 0.7 x 1
108513 Nexona 65 1 x 1
103056 Overking Bathezid 65 5 x 1
108510 Phara Dar 66 1 x 1
103080 Prince Selrach Di`zok 61 0.5 x 1
103055 Queen Velazul Di`zok 62 0.5 x 1
89001 sebilite protector 60 1.25 x 1
94009 Severilous 60 3 x 1
108509 Silverwing 66 1 x 1
91093 Talendor 60 2 x 1
89000 Tolapumj 60 4 x 1
89154 Trakanon 65 4 x 1
108511 Xygoz 65 1 x 1
A few additional creatures drop it when Velious and Chardok revamp hit, but I'm guessing this is a close approximation of the odds on this server. I don't think reavers drop it.
(Edited):
-Changed the theoretic drop chance off Ixiblat, as it was misleadingly high. Should be closer to accurate now.
-Not sure if "sebilite juggernaut" has a chance at Torpor. I think that is where I got mine, but maybe I am mis-remembering and it was off the protector. If they do have it, it is an abysmally small chance at it.