missed the 10 year aniversery

The formula for the macro is this:

1. Press key Space
2. Pause execution for 510 ms.
3. Release key Space
4. Pause execution for 2190 ms.

Set this macro to be toggled by a button press and repeating constantly. I used a Corsair keyboard for this, depending on what you use the terminology might be a little different, but the most important thing are the timings. Start the loop at the right moment, as if you were starting to press space to jump over the pit, which is halfway between it and the right wall. Player 1 will jump autonomously and you'll be free to focus on jumping with Player 2.

I just got the achievement using these tactics, it took me about 4.4 hours over two days.
I hope that helps and you can manage this too! Feel free to add any of this info to the guide if you want.

Cheers!

VI. As Kibaro pointed out in the comments, the hardest level is "Get a Move On" in the Gallery, because it requires precise timed button presses for both players. But fear not, because Player 1 only ever has to jump over a single hole in a loop, over and over again. You know what that means? It means you can make a macro for it. You can use whatever software you want for this. If you have a "gaming" keyboard it probably has this functionality provided, but if not then there are free programs you can find online that will do basically the same.

V. My advice regarding default key mapping:

Action: E / Numpad 7
Up: W / Numpad 8
Left: A / Numpad 4
Right: D / Numpad 6
Down: S / Numpad 5
Jump: Space / Numpad 0

Provided you have a standard keyboard with a numeric keypad, i find these controls most comfy - jump is easy to press quickly for both characters and they are somewhat mirrored, which means that you use the same fingers for the same actions and this will make your muscle memory work better.

III. Do not hesitate to remap controls between the two players if you're trying to beat a level that locks you in two different chambers and it's confusing because of how players are placed - for example if you need to manipulate one character on the RIGHT side while using WASD. Always tailor your controls to what you need at the moment, even if it seems like a chore it will pay off.

IV. Some levels are either MIRRORED or they technically only require one player to get all the gems and there are no switches that need someone to stand on them. For these remember that you can actually map controls for both characters to the same keys! This is especially helpful for those levels where you are followed by your ghosts that kill you on contact - map both players to same keys and run into a wall and viola - You are controlling two in the same place, with one hand.

This guide really doesn't provide any useful tips... Anyone can figure out that you can play this with each hand on the keyboard controlling one character.
I can confirm that every single level can be completed without a second player, with a little bit of trickery. My advice would be:

I. If you don't see any mosquitos or threatening spikey balls going your way in a confined space, just take it nice, slow and easy and meditate on the level. Without imminent danger there's no need to rush.

II. Remember that mosquitos fly on a set path which is the same every time and resets when you die. In most cases there are safe spaces to be found in the level where you can "park" one of the characters without fear of being bitten by a mosquito while you focus on the other character.

nice

if you play the stage enough times you will see that the mosquitos actually have a pattern that they will always fly :) just keep an eye on the lookout;D

Curse the mosquitoes!!

If not this FU***** mosquitos that flying sooooo fu**** random playing with two at the same time would be so easy >.>