Thank you so much for playing! Indeed, the game is quiet hard and lots of mechanics are "not clear", we will try to improve the game in the future! We will try to reduce the hp cost of the laser and add more interesting mechanics ;)
You were definately on the right track, in our design the ideal loop is:
dodge bullet - open chest (spaming E)- hold you fire till the mutiplier become really high (mouse) - jump right before the floor break to achieve a perfect landing! (Space )
And it is up to the player to find the right moment to stop the laser charging to avoid overkill (I admit overkill is super fun)