What are the best mod crystals for this one?

If the best mod crystal combo exists, I'm not sure that I use it. I choose the mod crystals depending on my opponent. A default combo I use would be a couple of parched baguette crystals, blessing of natural armor tear crystal and critical strike tear crystal. But the parched and BONA are unnecessary if freezing/stealing are disabled.

Right now I have four Water Brilliant Crystals attached because I needed the extra water attack for an opponent. I'll likely change that again the next time I need to use the weapon for a tougher opponent. I try not to attach the really expensive mod crystals because I find that I change the crystals too much for that.

The critical strike tear crystal and The blessing of natural armor are the ones I also use the most of the time for my weapons. A good water weapon I use is Riptide, until now I am fine with this one too, and for some opponents for me it works fine together with Malignant Rift Staff. I just got the Trident and I do not have much experience with this one yet.

Thank you for your advice. The water crystals are a good idea and I will try them out also.

If freezing is enabled, you'll definitely want a parched baguette crystal to protect you from getting frozen. Other than that, it's really just about finding what works for different opponents. I was battling an opponent that didn't block water, so that's why I equipped so many water crystals. Good luck and enjoy your new weapon!

I like to use two parched baguettes on mine since they prevent freezing and do added water damage. My other two slots I use for attack EoR to do additional damage. I have a water and magma one on their to bump up its base attack.