If you want to be a monster-in-law, here are some things you can do. This is for the male's side monster-in-law:
1) Ask your son-in-law how much money he makes;
2) Ask your daugther how many times she has sex (to check the virility of your son-in-law)
3) Get his underwears and wash and iron it, then, nag him about his tattered underwears.
4) Ask him often if your daughter is pregnant, and if not, give killer stares to his groin area.
5) Boil ginseng for him, buy it at his expenses, of course. And while he is drinking it, tell him it is mean to produce grandsons.
Ok, that's all I can think of right now because my mom is such a good mother-in-law to my husband. But if you ask me about my version of monster-in-law, I think I can list 100.