On the level The Hilltop Mausoleum, you must work through the level to the end of it, then head into your inventory with touchpad and select your arm. You can then throw your arm (
) at the Stained Glass Demon's heart when it is exposed to do damage. Dodging his other attacks in-between. You can switch to another weapon to use your shield, just don't do any damage with the other weapon. You can get around 5-7 throws in per heart exposure, although as the fight goes on, he starts to rotate when exposing his heart which may mean repositioning which will cause you to get less hits in. Each attack with the arm does 10 damage and he has 500 health so it will take 50 hits to win the fight and this trophy.
Note, the level does not end until you leave through the hole in the window. So if you miss the chalice, don't worry, you can still go back and complete it after the fight.
A quick guide through the level if you need it:
*** Spoiler - click to reveal ***Clear the enemies of the first area, grab the Club from the chest and use it on the glowing coffin lid to continue. Follow the new area and smash through the glass, clearing the enemies out and then go left first. Clear this area out and grab the Earth ruin. Now run back out as the floor will collapse.
Now take the middle path. Clear the enemies out and head up the stairs. Go through the doorway and grab the Moon ruin. Then head into the room on the right and grab the Chaos ruin.
Skip this paragraph if you don't want to get the Chalice: At this point I would recommend heading back into the previous room and through the gate at the bottom of the screen. This leads back to the start where you can drop back down the coffin and take the right path. Doing so will allow you to grab the sheet music (the floor will collapse again so run back) that you can take to the guy playing the piano in the room you grabbed the Chaos ruin. To get back to him, go back through the middle path, up the stairs and through the next 2 doorways on the right. Go up to him, open your inventory with the touchpad and select the sheet music. He will open a door where the Chalice is and some coins.
From the room with the piano player, head left and left again. Go back down the stairs and to the bottom right of the room. Go through the door opened by the Chaos room and clear out the enemies. Now push the platform that has fire on top of it. Once you get it around the corner and to the floating crystal heart you will unlock the boss upstairs which you can go fight as per information above.