I constantly see these on Smogon, and I am wondering how they work and what EV spread in HP is needed. How?

Edit: ok i didnt explain it very well, this is what i should of added. It soesnt have to be 100 base hp with 252 evs its hp just normally is around 404/405 which with the kyurem set is exactly what you get 405hp which allows you to use 4 subs.