Kluka
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He was supposed to attack the guard before visiting the structure. He landed on the structure, and his turn ended? No problem, we'll attack on the next turn and only then buy units in the structure.
But it's not that important; if there's flight, it means there's already a significant army, and the guard of the structure shouldn't pose any problems. Therefore, we can attack even after visiting. But we need to attack, definitely.
The guard also doesn't pose any problems. But the approximately 400 movement points spent on attacking it almost cost me that game.