Each attempt targets the Crab's current stage, at no gold cost: destroying its main reactor moves it to the next stage, with a harder base newly trapped with experimental defenses. Damage dealt to a stage carries over between attempts, so you can pick up the assault where you left off. You start with 3 attempts, up to 8 by clearing stages or waiting (one refills every 2h30). Rewards (resources, modules, crystals) increase with progress, up to the trophy tiers below.