P. Flame

P. Flame or Purple Flame. Required to finish the game without prior knowledge or glitches.

Location

Deep in the dog area, requires you to deliver the Mock Disk to the shrine that unlocks the door to the flame. It is possible to bring the Mock Disk without obtaining the Disc, which allows you to skip the ghost dog chase.

Otherwise it is recommended to open up any many shortcuts as possible to make the trek as painless as possible. The ghost dog can also be lured away by using the shortcut room, which gives you plenty of time to do most of the run unopposed.