it;s good skill,
after resetting multiple times i finally understand that skill
the skill formula seems weird to me, probably works like Arm Cannon
but i lvled my other pala to rg using that skill, with 20k GC per hit to bunch of nub undeads in GH,
who need 3-5 hits? if you can ohko them with only 1 hit
then as RG, by job lv 2-6, i able to unlock Piety. makes your armor holy element
makes you immune to GC negative effect, so you can still use your armor like tao or anything
GC also works with eddga and BP, and the way you tank while casting that skill it makes BP procs so often
Guard proc doesnt cancel GC skill while it does on other skills- even lvl 10 one works like a charm for grandcrossing
MATK part element is holy , so if you cast it on normal/other element mobs it does silly damage, but this part is dominant in gc formula
ATK part is pseudo elemental, you can use converter but it will increase only some part of it
MATK part works better for undead, pump a lot of matk will increase the damage by a lot to undead / weak to holy monsters ( tested with RM boot )
while ATK part works better for normal / other element mobs because of converter lol
for normal type, i lvled my rg in nogg using Giant Shield + Earth Drive till 125
the only downside of this skill is i need to go back to entrance every 10 mins, just to recast FCP
the rest is good, with shield spell lv 1, elemental advantage and some tricks, it can jump to 60-70k AoE in abyss lake 2
i lved there until 140