E3S9: Use empty SLF to match the entire map for [remove_item]
E3S9: Implement cave/hive ambience sounds, SFX fade-out sequences included
E3S8C, E3S9, E3S10: Increase AI aggression from 1.0 to 9.0

According to mattsc, at aggression > 1.0, the AI will favor attacks
which increase chances of its own units being damaged by the opponent.
At this point of the campaign this should be a Good Thing™ since it
increases the chances the AI will lower Elynia or Elyssa's HP during
boss encounters while making it easier for the player to kill its units.
E3S9: Rewrite last dialogue line

This is not intended to be the full prose revision for this scenario.
Yes, I'm looking at you, 8680.