This can be earned even earlier, at the very beginning of Painting 7 in 'Teensies in Trouble' - "Breathing Fire!"
From the start, jump right up the two rings, free the teensie (if you wish), then jump down. There will be a lava pit, and enemies dropping from the sky with parachutes. Stand on the left edge of the pit, charge up your attack by holding "X", then release it as one (often two) cross it's path. They drop continuously, so just stay there until you hit 5, and the achievement will pop.