Open regedit.
(WIN+R, then type REGEDIT, then press enter key)

Find:
HKEY_CURRENT_USER\Software\Bogdaneh\Unlikely STICKMAN

Edit this term:
BOOSTER_KILL_h705268554
to any value you want. (I suggest at least 54 hex, or 84 dec)

Open the game.

Go to level 1 (or any other levels with only 1 enemy.)

Click the green pause button on the top right:

Click on the the skull (on the right, above "resume"):

Then you automatically win and get 60 achievements.

Restart the game, play it for 84 times and you should get all 5000 of them.

Have fun.

Thanks to Vule for telling me that repeating the same stage can get achievements.