On any enemy, but if it's an elemental attack, and the enemy has protection for that, then they'll either take half damage, no damage, or absorb it. For example, Beta is fire based, so using it on a Bomb would only heal it, since Bombs absorb fire. That being said, most (if not, all) bosses are immune to gravity attacks, and the E. Skill Laser is gravity based, so they won't work on most bosses (just FYI).