use a bow or bowgun at medium range (out of range of his hipcheck or tail). it'll fire
water shots at you which you just need to roll to avoid, you can normally tell he's going
to do it. If he goes in the water use a crag shot or sonic bomb to get him out. you can
use pifalls on him to keep him still.

If this is the G rank plessy your fighting things become alot (i mean alot) harder.

If your not fond of a Bow/gun.. he can be killed simply with a Great Sword just stay slow
steady, decorate your fav armor with Auto gaurd and life will be alot simpler till you
learn his movement.
Ive killed him with just about everytype of weapon pleth is a wyvern you just cant rush
really.

get your best armor with auto guard.The weapon I use is twin blades.When de does his
hipcheck move(which has retarted range)wait after he does that,run under his his
legs.Attack his left leg so the tail cant hit you,then go to town on him until he falls
down.When he falls down attack its head.

Things you should bring is
Demondrugs,Armorskin,potions,megapotions,herbs,blue
mushrooms,honey,maxpotion,whetstones,(you must have)power juice),sonic bombs,some
traps.Good Luck

get a gs(great sword) and stand under him and before you land and atack always charge the
gs to the max.Be sure to paintball him so you can track him