Different iterations are triggered by finding certain key items in the previous iteration.
Iteration 0 Edit
The goal here is to find the key to The Studio. It is located on the desk in The Study. This is the only iteration in which the house can be freely explored (with the exception of some locked doors), and the only iteration free of any visual or auditory hallucinations (unless you count the Rat).
Iteration 1 Edit
Iteration 2 Edit
The goal here is to find the second key item, a vial of blood. It is located in the Bedroom.
Iteration 3 Edit
The goal here is to find the third key item, a box containing a bone. It is located in the Basement.
Iteration 4 Edit
The goal here is to find the fourth key item, a lock of hair. It is located in the Nursery.
Iteration 5 Edit
The goal here is to find the fifth key item, which is a finger.
Iteration 6 Edit
The goal here is to find the sixth key item, which is an eyeball. It is located in the Bathroom.
What the Magnum Opus actually becomes and is is determined by the player's actions throughout the game, triggering different Endings. There are three different paintings that the Magnum Opus can be (one of them creating an infinite loop of creating the painting again and again).
The Neutral Ending (achieved by picking up as little items as possible and only "dying" once) will give you a painting of what appears to be the Wife without any disfigurement, but then the painting quickly changes into a sinister and skeletal looking being. The Artist exclaims his frustration, and throws it into a nearby room (showing that he has made the same type of painting repeated times).
The "Selfish" Ending (achieved through dying the least amount of times possible, following the rats, ignoring your wife at all times, and don't push the wheelchair) will have the Magnum Opus not be anything about the Artist's Wife or Child, but instead be a self-portrait. He'll exclaim his feat in a cheerful tone.
The "Selfless" Ending (achieved by picking up as many mementos as possible, going to your Wife as many times as you can, and pushing the wheelchair in the hallway) has the Magnum Opus become a portrait of the Artist's Wife and Child. Differing this painting from the "Neutral" one is that the Wife and Child remain beautiful and do not become skeletal, yet the artist will still feel defeated through his continued dialog. The Artist then takes the painting, goes upstairs to what is presumed to be an attic, and the player sees that the Artist has made many similar paintings of his Wife. He lights them on fire, throwing the newly made painting into the inferno and then tossing himself in.