In fallout 3 I would have loved to have seen a were-yao gui but for NV I think a were deathclaw would be awesome, where you get bit by a deathclaw and every night at 7.00pm you become a deathclaw and can go around killing people with no karma or faction penalty, but if anyone sees you change they will try to kill you in human form, might be too difficult to do but if any one can do it Id love to see an end result.