Aside from the Sailor pathway's Raging Blow, Alger knew that he didn't have any powers that were adequate against the six-winged gargoyle's strong body due to its immunity to lightning strikes.
Of course, directly creating a resonance with its hearing organs and Body of Heart and Mind through the use of his singing was the most effective method. If this encounter had been anywhere else, Alger definitely would've exploited the gargoyle's great weight and lack of agility to circle around it. Then, as he sang to affect it, he would attack the same spot with sharp wind blades, slowly grinding away at his enemy through the cumulative damage over time.