Mothra is a pretty powerful kaiju, but her abilities won’t be enough to stop Ness. Ness has some powerful PK abilities at his disposal and Mothra just won’t be able to compete with him. Mothra has some strong lasers of her own, but they would just be absorbed by Ness. Mothra is too big to try and hit Ness, so Ness can gradually reduce her health with punishing attacks. Ness wins.