Lvl.1, you just have to stretch your jumps, and control your height for some of them.

Lvl.2, the point here is, to land on the block's edge, beside the switches. On some screens, you can jump to the next screen, to reset the orange blocks on the current screen, if you're high enough. On the 3rd screen, you have to find the invisible block to get to the switch. Start your double-jump "before" pressing the switch, and after you press the switch, jump again... it's a trick used a few times troughout the game. Otherwise, the jump would be next to impossible, but this way it becomes easy.

Lvl.3, climb on the right to the 2nd screen, and time your jump so you land on the bottom orange block on the 1st screen. Watch out for a black (invisible) block on the 2nd screen. On the 3rd screen, the jump is hard, but can be timed right using the disappearing box at the bottom. 4th screen says it ALL: it spells "TRAP". If you can read it, you'll skip it and be fine. If you don't read, you'll eventually have to restart from the beginning (*and editing the save-file? I wouldn't cheat, but it's your own choice*). 5th screen has an invisible blue block on the bottom left, just watch out for the invisible switches.

Lvl4. On the 2nd screen, invisible block on the bottom left, and "1st save point". Climb to the Run expansion, then go back to the previous screen, and climb the right area of the screens. On the 4th screen, you'll have to do the double-jump I explained earlier. Jump to the switch, and after you've touched it, jump again, and you should go through the disappearing orange blocks, up to the gray blocks up right. On the 5th screen, 3 blocks are actually solid, one orange, and two blue blocks (a line block is on the right wall).

Lvl5. Jump from the right, to land on an invisible block in the middle. A second block is on the far left, and it will allow you to reach the "spring blocks" at the top. 2nd screen... if you've noticed in the 1st screen, the NEXT box said NEXT, which means an indentation in the right wall will let you jump to the top. Using the spring blocks, jump to the 3rd screen, under the gray blocks, to the spring blocks on the left, then jump back to the middle gray blocks. Watch out for the switch, and jump up to the 2nd save point, and the maze. Travel in the maze to the left, and double-jump (or spring jump) to the top. On the right of the maze, there will be spring-blocks to make you jump higher onto the next screen. On the 5th screen, if you haven't taken the yellow key, you can move on using a blue block at the far right, and the 2 yellow key-blocks. Note that in case you fall, there's a blue block right under the yellow-key block on the left.

Lvl6. 1st screen: it has a purple key-block line struck through the middle post, where you'll be able to go through once you have the purple key. If you fall all the way through, the first purple blocks at the bottom hide spring-blocks underneath. Climb the left side to the 2nd screen (the jump is hard but can be done). On the 2nd screen, press the switch, and where the orange blocks were, there are invisible springs. Use them to jump as far above as possible, either on the left or the right, because a line block will be in the middle of the 3rd screen. Walk through the middle post to reach the switch on the top right, and go back ON the middle post, to double-jump up to the 4th screen. BUT, carefully land on the orange block, beside the switch, back in the 3rd screen. From the orange block, you'll have enough jump height to reach an indentation in the blocks on the right, in the 4th screen. Jump onto the invisible blue block on the left, to reach the spring-blocks at the top. Use them to reach the center purple block on the 5th screen. Grab the purple key on the left, by going through a fake key-block in the middle. Don't forget the "3rd save point", under the key. Then, fall down to either the 1st screen, or the 3rd screen, where you can walk through the middle post, and when you get to the right, spring-jump where the purple blocks were, up to the 5th screen. There, the top white boxes are actually solid, except for the leftmost one. Time your jump just right to jump through that white box, and go through the middle post again, and reach the top. The trick is to use the springs to jump on the right of the "T" block... I mean, if Juni rebounds very quickly, you'll have a much harder time getting the proper height to reach the white box. Remember, it's supposed to be Hard, NOT Lunatic. If it's Lunatic, you're doing it plain wrong.

Lvl7. Fire and Ice. Now this is easy, if you practice, and if you follow the right "path".
1st screen: Jump on the fire-T-block (on the T part), and jump to the ice-line-block on the right... and use your double-jump when you are against the line to go THROUGH the ice-blocks, and again, double-jump to reach the top of the line. It takes control and patience (I can do it fairly easily, and I believe I'm human too). You may have to do more quick double jumps, as long as you reach the top of the line. Then, jump ONCE to the L-fire-block at the top. Double-jump to the T-fire-block on the 2nd screen, landing on the rightmost part of it.
2nd screen: Again, practice makes perfect. Jump from the T-block, THROUGH the 2 line-blocks, and when you get through it, double-jump again EITHER to the top-right if you have enough height, or up through the lines again if you need more height. But the goal is to reach the invisible blue L-block at the top right.
3rd screen: Just overhead is a square-fire-block, double-jump to it. Hold the A key to carefully position yourself on the edge of this block, and jump across the screen to land at the right of the switch. Watch out for not bumping your head. Then double-jump to the orange-fire-block overhead. Now, you can either jump straight to the leftmost fire-line-block, OR jump on the fire-block in the middle then the fire-line-block. Your choice.
4th screen: From the fire-line-block, jump onto the orange-L-block. Then, simply double-jump over the switch to the blue block, and then jump to the topmost block. Simple.
5th screen: From the 4th screen, jump to the L-ice-block holding the right arrow key, to go through the blocks. If you don't succeed the first time, try to land on the blue block in the 4th screen, so it will be easy to go back to the 5th screen. While at the top of the L-block, jump once to the switch, and use your double-jump to come back to the L-block. Then, a simple double-jump will let you reach the top of the second L-block (slippery, remember). From the top of this L-block, jump to the next screen a "bit to the right", to reach a T-spring-block. Once there, the worst is over.

Lvl8, spring-jump to the top-right spring block, up to the 2nd screen. Then go back down to the "4th savepoint" of the game, on the orange-T-block. Look at the NEXT box... it suggests there's the umbrella item in the next screen... BUT it actually means to investigate the left wall, where 2 indentations make it possible to climb up to the 3rd screen, where the real umbrella is. So in the 2nd screen, climb to the top row of blocks, and double-jump to a blue block at the bottom right of the 3rd screen. Now go to the very top of this block, at the edge, and stretch a double-jump to reach the umbrella inside the wall. Now double-jump without the umbrella to the spring-blocks at the top, and open the umbrella at the peak of your double-jump. Spring jump to the left of the 4th screen, to an indentation between two blue blocks. Opening the umbrella after the double-jump always helps, giving you much more height. Climb to the top blue block, and ???... now you have to do a wallswim on purpose!  Look at the chess board squares, from the left, the 9-10th and 12-13th squares have gray blocks overhead. So double-jump to the 9th square (a dark square), and you should wall-swim through the block on the 5th screen. When in the 5th screen, fly down through the switches with the umbrella, and when you reach the 4th screen again, jump back through the 12th or 13th square to wall-swim through the second gray block. Then carefully climb the orange blocks, and jump to reach an hidden "5th savepoint" at the very left, inside the S-shaped block. Now double-jump to Lvl9.

Lvl9. Double-jump, and open your umbrella when inside the updraft. Try to gain as much height and speed as possible, to soar to a black (invisible) L-block on the far right. It will let you reach the top T-updraft. On the 2nd screen, all you need is momentum... you don't need the leftmost updraft at all... just use the line-shaped-updraft to reach the top-right S-shaped updraft. In the 3rd screen, use the updrafts, and don't get the key right now. Climb to the 4th screen, up to the green key-blocks. Try to keep soaring under the blocks left edge, and hold the left arrow, to soar to the yellow key in the 3rd screen on the left. Use the "6th savepoint", and take a deep breath. You need to go back down, with your new found umbrella, to the 1st screen of Lvl7, where the red key is located.

Lvl7. OK, first thing, lvl 7 is NOT buggy! You will get stuck inside fire blocks if you try to get through them with the umbrella... think of it like molten concrete. So follow the same path as the last time, and using the umbrella through ice-blocks, you should have an easier time getting up to lvl8. (Again, to make sure it's clear, you shouldn't keep the umbrella always open, or you'll have a hard time. Use it only in the right spots. The umbrella WILL get stuck on "molten concrete".

Lvl8, get through it just like the last time!

Lvl9, fly up to the green keylocks. You'll learn one important thing, and that is, the red keylocks generally have updrafts beneath them. So use the updraft to fly up left, and to the 5th screen. Lock Madness? Nooo. The NEXT box in the previous screen guides you to an S-shaped yellow-keyblock... so fly using the red keyblocks, through the updrafts, and reach a black (invisible) block just under the orange keylocks line. The rightmost purple keyblock is a fake, jump through it to it switches, and unlock the orange keylocks. Use the remaining green block, purple block, and blue block to reach lvl10, on the left.

Lvl10. Jump THROUGH the left wall in the first screen. Apparently, the left wall doesn't exist anymore from now on. Remember? The red locks generaly hide updrafts. So use your umbrella to fly using the hidden updraft, and soar to the 2nd screen upwards. Using the L-shaped updraft, gain height and speed, and fly to the right wall, where two updrafts are located (inside the wall). When you get to the top updraft, close your umbrella and land on a solid piece of the wall (this way, you'll recover your double-jump). Use the updraft, and then your double-jump, to reach a spring-block in the 3rd screen.
On the far left, there are two blue blocks... the top one will reveal itself when you get closer. From the top of it, do a leap of faith to the far right into the 4th screen, where a blue S-shaped block is located. Jump to the blue L block on the left. THE EYE! Grab it using your double-jump to get back on the L-block. And go back to the S-block at the bottom right. This next move will save you some trouble. Fall down to the 3rd screen, and double-jump EXACTLY when you've entered the screen, to get back up to the S-block. Ghost blocks should have now appeared. If you miss this last step, don't worry, just use the ghost blocks to get back up to the 4th screen. It's just a bit more tedious. Carefully jump up to the 5th screen (with the ghost blocks), to the "7th savepoint". When you've saved, jump onto the column on the left. Double-jumping from there will lead you to Lvl.11.

Lvl.11. Land on the L-gray-block. From its top, jump ONCE, and open the umbrella when you are inside the line-shaped updraft on the right. Hit the switch by closing and opening your umbrella quickly. Then finally, to get back to the L-block, use your double-jump. Now jump ONCE, through the updraft on the left (square-shaped), gain as much height as possible, and use your double-jump to enter the screen above. The purpose was to make the orange blocks appear again. So fall back to the 1st screen, and jump to a blue L-block on the right of the screen. Use it to jump to the S-shaped orange block on the 2nd screen. Now jump to the GRAVITY block on the left. It's called GRAVITY block, because you cannot jump when you're ON them. So when you are on it, open your umbrella, fall beside the GRAVITY block, and use your double-jump to reach the tip of the S-shaped updraft... if done correctly, you will gain enough height *moving toward the left* to reach hidden spring blocks, (just under where it's written L11). Using spring jumps, move to the 3rd screen.
THIS is GRAVITY screen. But it's not hard at all, I swear. All you have to do is drop from a block with the umbrella, and use the double-jump when you are beside it, so the gravity doesn't affect you. I can't help much more than that... You don't need to land on every box in there, shape your ascension the way it works better for you, up to the top most S-shaped block. Remember that you can't use the first jump here, only the double-jump.
When atop the S-block, do the same maneuver to reach a line shaped updraft, on the left in the 4th screen. (What you need to know: The switches do nothing, at least the visible ones. The green block is fake, and you can go through it. The gray block hides an updraft underneath, just like the red-keylocks. The orange-keylocks actually hide the switches themselves, to disable the orange blocks at the bottom.) So from the updraft, get onto the blue block just beside the fake switch. KEEP your double-jump. Jump once, hold the jump button, and fall with the umbrella, down through the green locks, and through the gray block. Using this updraft, you can reach the red locks (if you've kept the double-jump, this step will be easier). Land onto the orange blocks on the bottom right, and from there, close the umbrella, and double-jump through the orange locks to hit the switches. Soar down with the umbrella, to use the new springblocks. The springblocks will let you go all the way to the top of the screen... just move left, and enter the 5th screen.
This 5th screen is special, as it contains only simple orange blocks, and one of each Tetris shape. You can (in theory) only complete this screen by jumping at the right place. The right place is the bottom left S-shaped block. You need to be on the top of it... then, without the umbrella of course, juuuuump under the square-shaped block (going PAST it), douuuuuble-juuump under the L-shaped block, with a final hook to the left, and open your umbrella when you can touch the updraft above. It's in fact the hardest jump in the game (in my opinion, and in my multiple playthroughs). But although it's hard, I made it every single time, with a little patience.
When you reach the top, and final screen, a savepoint is hidden on the very left of the screen, inside the gray floor. All that is left to do, is, like the name of the 12th level suggests, The Final Countdown. Jump to the far right, and fall back to the first screen of the game. I leave the rest to you... and to beat my "highscore". ;)