It turns out the wyvern is easy in a not so confined space. I climbed up and led it down to near ground level where i was standing on a long flat platfrom. Easy way to beat it is to use a megashark and jump when it charges at you and aim down when shooting. land wait 5 sec then repeat. Of course this may not work for others because i was using demon wings. But in the end i won.
And it turns out it respawns and isn't a one time boss :(