A quick way of upgrading the flux rifle
First go to planet tobra and get out of the underground tunnels, you will see a old man go to him.
Once you have talked to him get out the flux rifle and another powerfull gun, start exploring when you get to the enemie with the electric tentrils
shoot it with the flux rifle with the small ones use the other gun (double tap triangle)keep doing this until it has upgraded.
Flux rifle-vapriser
Hope I helped
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