You need your dungeon upgrades to reinforced and then to get five werewolves lure. Find him then use them, win the fight after doing so and he should be yours.
you need 5 werewolve lures as the number of turns its affect lasts for is % chance of you capturing. so using it once is 25% chance but each time you use another you lose 1 turn of its effect so using 5 gives you 100% chance
