100 Doors 2 Level 86: Flip the pipes so they connect. There should be two different pipe sets. Connect the parts that show the smoke/gas over it to get rid of the gas.
100 Doors 2 Level 87 Walkthrough
100 Doors 2 Level 87: Pick up the knife and cut the two red strings holding down the animal pelt. Drag the animal pelt up to uncover the door.
100 Doors 2 Level 88 Walkthrough
100 Doors 2 Level 88: Tilt your phone to move the platform. Destroy all the blocks.
100 Doors 2 Level 89 Walkthrough
100 Doors 2 Level 89: Open the drawer, pick up the fish food, and put it into the tank. Wait for it to flip downward so the key sticks out of the water, then quickly tap the key to take it. Use the key on the door.
100 Doors 2 Level 90 Walkthrough
100 Doors 2 Level 90 Explanation 1: On each square there is a green line. Match up the green lines to slide the ball through each square to collect the coins. Once you have done this a black hole will appear and just line the green lines up like in the picture shown and the ball goes down and the door opens.
100 Doors 2 Level 90 Explanation 2: When you turn two box "doors" towards each other, you can "swipe" the ball in the direction you want it to go. You just have to be careful that the last box you were in's door is turned away from the next one after you move the ball, because otherwise, the ball just goes back into the last box. Once you have all the coins, a box will open that has a hole. Guide the ball to the hole, and you're done!
Special thanks to Jackie and Josie for this solution! You guys rock. :)