Give your player character Platform behaviour with default controls set to 'no'. Then in events you'll need logic like this:
Player is visible: Player>Platform>Simulate control>Pressing "right"
Player is on the floor + when 'Space' is pressed: Player>Platform>Simulate control>Jump
Player is not on the floor + when 'Space' is pressed: Player>Platform>Set gravity to 9999
When Player lands on the floor: Set gravity to 1500 (or whatever it was to start with)
That should do it