The thing about Leveticus is that whenever he dies, if he has any hollow waifs hanging around (generally there will be two, but if he has just the box there's only one), then it is sacrificed, then he comes back where it was, then it gets summoned again. So basically you need to kill both him and his hollow waifs in one turn to make sure he stays dead.
However, if your friend only has the box set, then you shouldn't have too much of a problem. The main part of the box set is 4 steampunk abominations, which can combine mid-game to summon a decidedly killy desolation engine. Luckily for you, the desolation engine isn't in the box.