necromancer froglok for dark rune

[mal4t20]

i camped this guy for 3 days killing him constantly and he has never dropped the 4th rune ever.
i could see if this was a high level quest but this is a noob necro quest. could anyone explain to me why its so damn rare?

 

[Wiz]

Resolved this.

 

[dasplund]

I've been camping this frog since thursday or friday (the 15th/16th) for about 6-10 hours a day, and haven't gotten the 4th rune yet. Is it still messed up? Also, with my iksar beast i was killing giant leeches that entire time in the swamp for part 2 of the beast quest (stunned leeches) and haven't gotten a single drop. I have gotten 4 or 5 stunned gators, but no leeches.