Head over to the north door and move to the banister to the right of it. Now align yourself so that you backflip into the small banister. Clip into the ledge and fall under. Then simply backwalk to the loading zone.
It is possible to go straight to Phantom Ganon fight as Child, using a TSC and some oob movement.
By catching something in a bottle on the same frame that the cutscene where the four poes leave the main room of the dungeon, you can walk around during the cutscene. With this you can get on the elevator before it disappears. Once on the elevator, sidehop or backflip to lower it.
You can store a Ground Jump using action swap from hookshot to bomb/chu and skip having to do the maze.
If you have Din's Fire, you can also use hookshot jumps and actor glitch to skip the block room, as well as one of the two keys.
You can use a bomb jump in order to land on the ledge in the block room, and walk out onto the balcony for the floormaster key.