here is something similar, but involves objects dropping and exploding but it can be any object, so could be tiny and almost unseeable or use an unseeable entity.
in other words..
choose any entity you want. in this example 'rock'
make sure entity is set to dynamic.
place your rock entity's in the air where you want your explosions to happen on map editor.
then right click on entitys, go down to where it asks ENTITY SPAWN AT START and type in no (spawn after delay)
on the same window go down to physics and change entity damage to minimum. ie 1
set damage type to explode on destroy
set weight to high so there is a heavy fall and creates damage on the entity's on impact. then apply and change to new settings.
then get your trigger zone, place where you want right click then main ai to plrinzoneuse script and bellow that in the if use box type in rock.
run game and have a look. this script is good for cave-ins, traps and any thing you want to drop down or explode.
hope this helps you
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