hmm.. i nv use bowgun 1 lei.
i always use my G.sword.
I think gravios weak element is water rite? or was it dragon...
Since now i got the water element Gsword (dunno how to spell the
weapon's name) i use it on most of the wyverns. Or else i will use
the eternal strife on dragon elemental weak wyverns.
maybe you can try using traps on the wyverns, works on most of
them, except on 2nd attempts on trapping yian garuga.
Now i kinda stuck on Four Horns quest... so now playing around with
crafting weapons, some of them kinda cool sia... like cat's soul.
