WARNING! This game does not feature saves. Dedicate enough time if you want to play it through to the end.
A guide for the puzzle solutions and the missable achievement.
Boy: input 334
Guy: input 215
How to solve: This number is found by looking at the cube and communicating it to your partner.
Boy: from left to right: blue, black, white, purple
Guy: from left to right: turquoise, yellow, orange, pink
How to solve: These colors can be found when looking up the door frame and are meant for you, not your partner.
Guy stands on the stage so the Boy can crawl inside, then the Boy pushes levers 1, 6 and 8 up while pushing all others down.
How to solve: The number of bottles indicates which numbered lever it is for. The color of the bottles is connected to the color of the plates. When rotated to the their back, the plates show if a lever should be pushed up or down.
Boy: Communicate the color of the cup and how many ice cubes it has. Press the middle button to fill the cup with the currently selected symbol, sometimes a certain symbol will require 2 fillings.
Guy: Find the right recipe for the correct cup, hitting play moves the cup once to the right.
Correctly fill 4 cups to solve this puzzle.
How to solve: Look around the room, for example the apple in the kitchen is in the first position, the red lever is moved to the first position (left). Second position for levers is middle, third is right.
Input the code 2679
How to solve: Guy stands on the weight, then the Boy can stand on the chess board. From here you can combine your notes to get the 4 digit password.
How to solve: Look out the window and find the symbols on the ship. Find the first symbol from the ship that matches the first position symbol on which mannequin. Use the color of the correctly matched mannequin on the top position on your model and work your way from top to bottom.
Puzzle 2: 4458 from top to bottom on the spinning wheel.
How to solve: Find the missing numbers to fill the board. Then do a calculation x+y-z for all numbers on the board in a column (top to bottom) to get the password.
Enter the ship by using the pressure plates
Puzzle 3: Guy sees the correct symbol, Boy has to select that symbol out of possible 4. Do it 6 times to solve this easy puzzle.
Puzzle 4: Combine the obstacles from both players, as both obstacles will need to be avoided. Boy moves up and down, Guy moves left and right. Reach X to win.
Thanks to FrozenShiver and Th3P4!n for his great guide, all credit to his effort. you can also read the original guide from Steam Community. enjoy the game.