In my career as a Bladedancer, i heard that is not good in PvP if you mean 1v1 PvP. I play on a C4 server, and the only classes i had beaten are other bd's, sws, BH, and really lucky a Gladiator...
But if you mean mass PvP or a group PvP BD is a must have, for mages party because of mystic, siren and concentration dances, and for archer parties because of fire,fury and warrior dances.
You can also help your party with hex and freezing strike. It's so much fun when target is running away and freezing strike lands
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If you mean equipment for C grade use full plate set, but i do not know much about good C grade duals
For B grade you must choose if you are going for more offense or more defense. If offense, choose BW set, if Defense, choose Doom set. All heavy of course.
For duals use sls*sls or sls*tsurugi, of you can try getting or making them +4
And for A grade there are also 2 options for armors. Tallum and Majestic.
Majestic - more defense, stun resist. Tallum - +2STR 8% atk.spd (makes a difference :p) For Duals use kesh*kesh or kesh*dama, best if plus +4.
Dama*Dama are useless, they have highest p.atk but shitty SA. Myself i use kesha duals +4, i like that bonus attack speed.
just don't hurry and use it too fast.medusa only works on flagged enemies.