This is one of the easiest things you can do. Make an action block that detects a condition, and when it’s reached do command F6 once, then continue on (and usually 05FD0001 to permanently end the action block). The simplest form is shown below, which just starts explosions as soon as the level starts. Make sure you do a 05FD0001 (or at the least, only execute F6 once, you can do more code), otherwise it keeps trying to trigger explosions every time it sees F6, and never actually gets far enough to do so.