this is only a short desciption how and where you can gain a missable achievement

Too difficult! - die, first time you can do this is in level 1, jump in the "black" water

I didn't even sweat - speedrun part, you can do this in level 2, solve the level in under 25 seconds

Can you jump over here? - i did it in level 4, do a elevator jump to the plattform with the button (right side of the room, the button activate the elevator and makes a green light to the exit door), the button to drive the elevator up and down is on the bottom of the elevator shaft. it is a little bit tricky because you have to jump forward and change reality to the same time and you need a little bit timing, or you jump not high and/or wide enough

It was unexpected - level 5, direct in the start area, jump to the door with the exit sign (yes you can do this)

It was necessary to be careful - i did in @ level 5, room with black water, well, die with the jump to the second plattform and/or die with the jump to the floating plattform, or fall from the floating plattform in the "black" water (dont know exactly what i did)

Good elevator - level 7, you have to press the button that open the exit door - do a elevator jump to the plattform with this button, a little bit tricky, because the game need a bit time to drop the achievement

It's light enough - level 8, in the second room, on the left side, there is a little "room" with a portal and a button in it and a button on top, well, go on top of the "room" (without the cube) and change reality to glass board

Here it is! - level 8, second room, where you found the cube on the left side (use the "jump pad" on the ground floor and switch the realities really fast, to land on the upper ledge). there is a hidden spot of the right side, where you can fall down in a corridor with a portal at the end.