While largely similar to the regular Spin Attack, the Bounce Attack consist of Shadow the Hedgehog rapidly attacking with a barrage of multiple Spin Attacks around his target, albeit with less power, as opposed to attacking once with one massive attack.
When his Spin Attack did not work against the Scarship, Shadow the Hedgehog resorted to the Bounce Attack, which worked better, as it damaged the ship from the inside with reverberations, although only briefly.
↑Masaki, Hiro. "Ship of Doom (Japanese dub)". Sonic X. Season 3. Episode 61. "Dr. Eggman: Shadow's Bounce Attack creates reverberations inside the Hellship, destroying it from the inside."