I can't use Ness for shit. I think CHarlizard is god tier.
isn't that great either.
Ness is my main, but I understand people who have problems with his style. To me, he's all about harassment and knowing what situation you're in at all times so you can either punish, retreat, or keep harassing. His biggest weakness is that he doesn't have any safe landing options; characters like C. Falc can punish landings and most of Ness's moveset from the middle of the stage.
PK Fire is super when you catch someone with it and can follow it up with a down throw > forward air > forward air > forward air, but this only works at low percentages, and only if your opponent doesn't hold up or back as you throw them (try to throw them at the same time you grab them so they have a harder time reacting). But don't spam PK Fire if your opponent is shielding them at close range; you'll get punished every time.
PK Thunder is your main harassment tool. The most obvious tactic is to toss your opponent into the air, then nail them with as many PK Thunders as you can until they land. If your opponent is coming back from the side of the stage, and you know they're going to make it with ease, be sure to try to hit them with the tail of the PK Thunder in order to throw off their rhythm: it passes through moves that the head won't. Use it to punish reckless dash-ins and keep space between yourself and the opponent until you're in a good position to approach. Don't hesitate to occasionally use it as a close-range tool in the air or on the ground, too. Don't use it to shoot yourself at your opponent unless you're sure it will hit. That is a good way to get killed.
PK Flash is a so-so edge guarding tool; send it low below the edge against characters like Link and Marth who have to travel a distance upward while vulnerable in order to recover, and try to catch them between the start and endpoints of their up b. One of my favorite damage-building tactics is to back-throw an opponent at low percentage, and if they try to jump back over you, hit them with an uncharged PK Flash.
Ness's aerials are great. Back air kills from the edge of the stage at 120-130%. If you predict an opponent's jump, nail it with forward air, then another forward air if possible. You can catch a lot of people during their approach with a fast-falling neutral air, or in the air if you manage to navigate to their sides, but keep in mind Ness's stubby arms are simply outranged by some characters in the air. Up air should be used sparingly as a surprise kill move for opponents expecting a PK Thunder, or comboed into from down-throw if your opponent tries to DI over you. Down air is a great spike, but hard to use effectively until you get a feel for Ness's falling speed. Try running off the edge of the stage while the opponent is below you and hitting them with a back-air or neutral air. Save your second jump so you can hop back onstage. You can also catch some opponents recovering from above with a neutral air; this is a great way to handle Little Mac.
And always remember that back throw, yo-yo, and bat are the way, the truth, and the light.