Welcome to the official walkthrough for "A Game of Life and Death"! I would ordinarily insist on all readers attempting a playthrough without a walkthrough first, but I did make this game fairly difficult, so I feel it's more than justified here. 
I am going to be guiding you through the "extended path" which leads to what are actually recognized as "alternate" endings to the game, even though they are much larger. There are three main endings, three alternate endings, one side ending, multiple "bad" endings, and several "game over" pages. The amount of branching paths and choices were created so that you, the reader, could explore and replay again and again. Have fun! 
Now, without any further ado... 
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So it starts...
At school: First, pick up your backpack. (You cannot leave school until you do.)
Using your backpack takes you to a separate inventory. Pick up all the items to take them out of your backpack. Noting the item descriptions will help you solve some of the puzzles. (Or just amuse you.) Before you leave, check your locker via the bottom link. It will provide you with a dirty photograph.  
Cemetery: You have one objective here. Obtaining the Coyote Medallion piece of Humility. The answer is easy: Apologize to the coyote god. Accept the silver piece from him and he will send you back to the start of the game.  You'll still have all of your items, so don't worry. 
The ice cream shop:  You can obtain a key item here. The Medallion piece of Compassion. There's another place where you can find it, but there's is no penalty for getting it early on and I encourage it. To do so: Go up to the little boy with hiccups, use the water.
In exchange for the water, the boy will not only give you the medallion piece, but will also give you a hint on how to solve the puzzle you could've used your water on. (Optional: If you do this, you may want to go to the machines and use your change to buy stickers.) Go up to the counter and get the ice cream. 
Now you need to pick a path to the house. Technically, there is no wrong way, but the more rewarding way is to visit your friends. You can visit either friend first, but you'll end up going to both of their houses. To save time and avoid a possible game over, visit Layne first. 
Layne's House: Sneak around to Layne's room and pick up the hoodie. 
Melissa's House: Sneak around to her window. You will learn the driving force of the plot in this game. If you show the hoodie to Melissa, she will explain that Layne is already in the haunted house and suggests that he needs you. 
The Witch's House: You can go in multiple rooms and get items in many different orders and combinations (unless an item is required to get into a specific room) so, I'm just telling you how I would do it.
Bathroom: Open the cabinet, take the crowbar. Check the sink. Upon looking into the mirror, you will be given a personality quiz. This quiz determines what your character's appearance is, but much more importantly, it determines what weapon you'll receive later on AND, as a result, which path to the ending you will be able to survive. Again, there are no wrong answers, all the weapons you could get can keep you alive, but for this playthrough... 
We're going to go through what is arguably the simplest path-- Broadsword. Choose "I'm brave" if you're a guy and "my courage" if you're a girl. Choose "I'm strong and all offense--I attack head on, no hesitation, no fear" for the second question. Choose "Martial Arts Dojo" for the third. 
The library: The desk gives you a porcupine quill, but you do not need it. If you read the book on the table, you get a hint to one of the riddles later on. Looking at the books hidden under the table gives you hints as to which weapons go with which pathway. On top of the table is a dish filled with mints. You may take some. Examine the book shelves and you can place your English Literature book here. Place the book between the second pair. You'll receive a small key. 
Dining room: There's nothing important here except for a hint in the china cabinet. Go outside. 
Backyard: Take special note of the fountain statue, it will be important later on. You can take the wolf's bane (but you don't need it.) Examine the rest of the backyard to get the shovel. Go back inside.
Now's as good a time as any to go upstairs, so return to the foyer, then go upstairs. 
Upstairs Hall: You need to go into the dark room first. 
Dark Room: Use your flashlight to receive clues from the walls of the room. Thishould warn you about a few things not to do. (Such as taking both items. This is the trial of "greed" that the poem talks about. If you try it, you WILL die.)Take the mirror. Do NOT use the mirror on yourself. Now, return to the hall and go to the second room on the right. 
Second room the right:  Select "not interested." Use the mirror.  Look into the coffin. Collect the skull. Look behind the skull. Collect the silver piece. (If you did not use the water earlier, go into the first door on the right and use it there. Pick up the silver piece. Otherwise, if you want to, use the sticker in that room... but this part is optional.) Head back downstairs.
Kitchen: You can explore in here, but it's at your own risk. Your goal is the pantry.
Pantry: You can grab the stomach. (You don't need it.) Examine the door and unlock it with the key from the library. Go through the passage until you reach the lab.
The lab: lots of little goodies in here. Check the shelves (upper and lower) to receive a bottle of glowing fluid, a bottle of poison, a deflection potion, a transformation potion. Check the counter, in the boxes, and under the boxes to find an empty flask, an empty beaker, a bug shell.
With either the flask or the beaker (or both) go over to the vat. Fill one of them with liquid nitrogen. Look in your backpack, pour the liquid nitrogen on the gum-covered silver piece to collect it. You're almost ready to form the completed Coyote medallion, but you still need that gum taken off. Go back through the passage-way.
Pantry: Slide open the side panel to the door. Use the dried bug shell (not the quill for this route) and the glowing potion. It doesn't matter which you put in first. Put the backpack in the chamber. Go ahead and go to the living room.
Living Room: Examine the fireplace and read the writing. Answer the riddles. (The answers are: Fish. Coffin. Water. Fire. Earth. Wind.) A trap will be sprung once you give all the correct answers. Your correct options are: Use crowbar, use shovel, use skull. For this route, it does not matter which you pick. Go down to the end of the puzzle and retrieve the mechanical lever. Go back into the living room, examine the couch, move the couch away from the wall. Use the lever. Pull lever. Retrieve the knowledge you receive.
Laboratory: Use the purple potion on your backpack. Go up to the new door that has appeared in the lab. You can use either your backpack or the crowbar to break down the door. 
Surgical Room: Take the scalpel and read the note. Take your new knowledge with you. 
Kitchen: Use the scalpel on the gum covered silver piece and pick up the last piece of the medallion, "Cunning." Go back outside and examine the fountain. You will be tested by the coyote god.  (The correct answers are: The Seven Deadly Sins. The names of the medallion pieces you just collected. Your backpack.) Congratulations, you now have the fully completed medallion of the coyote god. 
Upstairs: Feel along the walls and you'll find the testing room door. You cannot use your crowbar to open this door, only a transformed backpack will open it. Inside the room is the witch's daughter. She will kill you if you do not stop her. You can use your shell backpack on her. Once she's dead, take her key and cloak. Ordinarily, at this point, you'd be ready to fight a boss in the attic. However... to give you the full experience... we are going to the basement instead. 
Go back downstairs and then go down to the basement door. Once you get through the door, there is no turning back. You character will refuse to leave the basement until your quest is complete, so anything you'd like to try in the house, do it now or not at all. Now is also a good time to eat your ice cream and mints if you still have them. They will give you a boost for later on which may end up saving your life. 
Now, bash through the door by using your backpack. 
Basement: Go down the stairs. Congratulations, you've found Layne, but something is clearly wrong with him. Do not talk to him just yet. Instead, read the books on the upper and lower shelves. Take the diagram of bones and take the spirit spell. Read the witch's spellbook. You'll find it's locked. Use the key you took off her daughter's corpse and take the spell you find there. Now, and this is VERY important, go to the altar and arrange the bones in the pattern that the diagram shows you. 
Now you may talk to Layne. Keep talking to him. You will find out he is possessed by the ghost of the witch. Use the spirit separation spell to fight her on equal terms. You will automatically get a link to your spirit weapon, which should be the broadsword. 
Broadsword Battle: There are many choices throughout this battle. There is not always a "right" answer, but I will tell you to select the safest choices. You should also take note of an endurance count on the bottom of each page, kind of like a health bar. That count will remain unless the battle ends or you die. 
Choose: Charge forward. Flee above ground. Step through the west mirror. Go left. Hide behind the warriors. Apologize to the woman. You are now in a fight ring. Uh oh. Fight the witch head on. Chase after her. Defend yourself. The next few links, provided you have all the items and have done everything as I've instructed, will automatically lead you back to Layne and then, to Melissa. 
Lastly, depending on which of the alternative ending scenes you want to read... 
Choose either... 
Thought number 1: which leads to: Friends, Hold the benefits. (Your character is not in love.) 
Thought number 2: Which leads to: My hero/ine. (Your character is in love with Melissa.) 
Thought number 3: Which leads to: Traveling Partner. (Your character is in love with Layne.) 

Each ending has a little reward at the end of it for all your hard work. (Layne's ending allows you to see the concept art for his character. Melissa's ending also has the concept art for her character. If you get a perfect score on one of the quizzes in the game, the platonic ending leads to a third "hidden" love interest.) 
Congratulations! You have completed "A Game of Life and Death"! This game is over 1000 pages long in its entirety and was made with replayability in mind. Please, feel free to come back and try different pathways. There are many, many other potential endings which cannot be reached using (or -just- using) the steps I provided for you. Try to find them all. =D