I used:
*Powered Hydra (it can be used whether in short range or in long range)
*Long Barrel
*Blizzard Materia (ready equiped to get rid soldiers with barrier or big boss or something like that)
*Auto reloader (Err, you know, the ammo of this hydra is pretty suck. Only 5 ammo in P hydra, 3 ammo in P hydra Gamma, and 1 ammo in Gigant Hydra--And I want to customized it into Gigant Hydra(I have doubt on this one because of its speed only 1!!!) or P Hydra Gamma)