[member="Krafurk Maris"]
I'm not sure why a rogue padawan would know Force Crush, but presumably it wouldn't do much at all. Unless you're using art of the small you're not going to be precise enough to target the gas molecules where they can't simply slip somewhere else. As for killing them, as [member="Mrrew"] said earlier energy weapons are the best option. Blasters and lightsabers do a fair bit of damage(though I'm not sure if they'd have pain, as I'm not sure a gasseous being would technically have nerves per se). A flamethrower might due well also, burn parts of the Filar Nitzan individually. Also, if you can manage to make it extremely cold than they'd turn into a more liquid or even solid form, likely killing them.