Originally Posted by Dread  Im going to learn them both anyways but i can only learn 1 now which 1 would be better since monster for 3rd job are a pain and i don't have Shuriken...oh yah for fox... |
Landmine. Debuffs are "luxury" skills. Since I assume you are going Thief Master, Landmine actually opens up a skill you might be maining
because you don't have Shuriken: Explosives Expert.
Gloomy Mist, however (and by Gloomy Mist, I mean the alternative to Landmine in your thread title), is very situational in many ways, somewhat expensive to continually recast, especially when you don't need it, and only opens up more luxury skills for you (if I'm not mistaken, lvl 10 Gloomy is needed to unlock the Hide/Sudden Attack path).
Personally, I'd get Landmine to get Explosives Expert, go
back to learn Shuriken (because the next batch of skills provides a powerful multi-target Shuriken skill that should also greatly improve your performance), and only then focus on Gloomy and the other skills. But, as I've said, this is my personal opinion.