Well as I live in FL players tend to lead towards floaty characters (Samus mostly) and from my experience Mario has a slight advantage against Ness...
PK Fire and every other projectile can be caped, Ness' weight is within decent combo range, perfect Fireball aim eats PK thunder when recovering, I have found if you cape Ness when he's in the air doing PK thunder it sends him up just out of range of hitting himself. However, Ness' PK thunder recovery next to impossible to cape and will usually lead to you getting blasted away if tried, and there is the Yo-Yo Glitch (Slim but still possible)
I helped a little lol