Drop 5 bombs on yourself
Easier than it seems. If you fly from left to right, you will see that the bombs will come out above you rather than below. Go to the top left of a level and fly to the bottom right very slow. Drop bombs as you do this and you will hit yourself with them. Set bubbles to 5 so that you do not need to do multiple sessions. This trophy is much easier to do with an idle second player.