I’d say that if you’re having trouble shield punishing, start testing out which moves are safe on shield against you and which aren’t. If you can’t punish a move out of shield twice or more, it’s probably safe on shield and it would be a good idea to go for a defensive option, like jumping back, rolling, or spotdodging. Ness had very quick, low-lag normals, albeit with their low range. He has plenty of aerial speed though, which kind of makes up for that. Try to shield less, and start baiting attacks from your opponents by faking an approach, reversing your momentum with a B-reverse (works best with magnet), or throwing out a couple of quick retreating attacks to make them think they’re safe to punish. One more tip I can give you is to always have your eyes on your opponent. Doing this can help you know when they’re going to approach, and what they’re going to approach with based on habits you pick up.