Does it hit for physical, special, or does it use the highest stat?
Gulp Missile's Arrokuda projectile deals 1/4 max HP damage and lowers the target's Defense 1 stage (Vengeance417)
Gulp Missile's Pikachu projectile deals 1/4 max HP damage and paralyzes the target (even Ground types) (GMars)
Source
It deals indirect damage. :P
Hope I helped!