There were already guides for episodes 1 and 2 but none for the third, so I made it! This will show you where to find all those diamonds to get the achievement for getting them all. If you have any questions please leave a comment below.

Get this diamond by entering from behind the fence and going to the left.

Easy pick after a platforming section.

Before the boar boss fight. Jump over the fence and get to one of the upper platform so you can access this spot from behind. The diamond is right below Tiny.

After another platforming section, an easy one.

While going up in the platforming section with the bats and the chains, break that wall to reveal the diamond.

Another easy pick.

Below the platforms after fighting the spiky blue enemies.

After the girls transform into blobs, get to the top by jumping from the right side of this section.

After killing the blobcat and ascending the first tower, get to this spot after jumping over some gears. The diamond is on the left side.

There are a series of walls trying to crush you here. After you get to the last part, after you picked the drumstick guarded by two zombies (just when the bats appear) start running to the right and try to jump into the upper section. You are safe if you stay in the middle of the platform. Break the block with the big coin to find another diamond.

When you get to the second monkey statue (the one with four hands guarded by two flying enemies) hit the hand on the right to get to this breakable wall.

Be careful with this one or the walls on the left will crush you. Take your time.

In this section you break walls to let the platforms ascend, being careful not to get crushed. Right before the end, go to the left and break one last wall so you can get to yet another breakable wall that contains the diamond. You must use the big platform that moves up to get here.

Yet another diamond hidden behind a giant platform. After the section with a lot of blue spiky enemies, go up with some chains to the right and start walking from right to left. A giant plaftorm will try to crush you. You must jump over it and smash the breakable wall very quickly so you can get to the diamond.

Inside the library you can get to this spot by climbing the rope on the upper side of the screen.

Jump over the invisible hole and get the diamond.

When you enter the room with the frozen monster, go back to the left and get to the breakable wall with the final diamond.