For this you just need a total of 4 hearts that aren't red (so either the pale blue or black hearts, any combination of them) to appear after your red hearts on your health bar. You must have them all at one time as well. If you have 3 black hearts and get hit, losing a black heart, you'll need to collect 2 more in that same run (without taking more damage) to get the trophy, they do not "stack".
There is an orbital buddy you get who looks like a little black ghost, his description basically says he wants to steal your hearts or something like that. If you're lucky enough to find him, let him pick up every red heart you see drop. He will start turning your red hearts into pale blue ones. If you find him on a run that decides to give you a bunch of red health, you could have this trophy in the first level or so (I got it on Basement 2 after finding said buddy on the first floor). Everything is random so it's a little luck based, but it shouldnt take too long to find the right combo of items.