You will not complete this on your first run even on casual. Come back with your NG+ save and when you get to the "survive the lycan attack" moment run all the way back to the waterwheel part of the map. Just continue taking out enemies and eventually the Urias(big scary hammer enemy) will spawn. Even after 4 runs of this section I could not hammer down what exactly causes him to spawn but just hold out and he will be there. Take him out and enjoy the spoils of your kill. In doing this you are also likely to get the challenge for killing 30 lycan.