Anti-air spell fired by the orc defenders, ineffective against the crawlers' gravity bombs.
As Party Planner releases its load over The King's Point, Louis reports that the defenders are firing their Flak spells — "but it's not good against gravity bombs."
He adds that they appear to have taxed their anti-air answering the Reaver missiles, which is part of why the castle's shield comes down further than expected. The real threat to the airship turns out to be not Flak but a long-range green death ray from a Synergy Towers emplacement.
Enemy anti-air magic that fails to stop the crawler bombing.