I'm making a custom sitrep for a map i made, where part of the mission involves a zone getting flooded, damaging all units inside. Is there a way to check the entire zone and apply an effect to every unit inside?

Yes, though it’s a bit convoluted. If you use an “emit trigger signal” effect, you can put a list of units (in this case the one that gets all units in a zone) in its “array” field. If you have another trigger set up to catch signals, it will trigger once for each unit in the former’s list with each unit in its context.unit field.

I can try and break that down into more detailed steps if needed, but hopefully that’ll point you in the right direction.

Thanks for the pointer, but would it also be possible to exclude flying mechs from this list? Doesn't make sense for a mech in the air to be affected by something on the ground.