1.add to the player bullet behavior
2.set bullet speed to 0
3.add a new invisible object above the ladder
4.add condition:on f pressed
5.add sub-event to the above condition:is overlapping with the ladder object
6.there will be multiple things that will happen when the sub-event is working: set platform speed to 0
Set bullet angle to above
Set bullet speed to whatever the speed you want
7.add condition:on collision with the object above the ladder
8.add events to the above condition: set platform speed to the default speed
Set bullet angle to default
Set bullet speed to 0
Hope you find it useful and understand what I mean.