Generally I've found that Ness is a +1 matchup for Bowser-and my area has quite a few Ness players. (and obviously, there's a crapton of them online). I'll list some things I've learned here.
- Bowser's greatest weakness against Ness is yo-yo edgeguards. I've found no definitive way to overcome this, so the best strategy to avoid it is just to stay onstage.
- Bowser can toughguy through PK Fire, making many of Ness' kill confirms less reliable-although it is a bit difficult. Learn which kill move Ness likes to go for (generally a smash attack or bthrow) and SDI while mashing an option to counter that kill move. Though I've found that once you go past 150, you're basically dead.
- Ness has about seven years of air time, but Bowser is secretly incredible at juggling, so this should not be too much of an issue. Up air tends to be a good tool here-and obviously if they start drifting out to avoid, just chase and fair.
- Ness has lots of combos, but no matter what, make sure you never go offstage because of them as I mentioned yo-yo earlier. DI accordingly to prevent any of that.
- Because Bowser is super fast, if Ness is about to PK Thunder back to stage, just run off and fair.
- Finally, using flamethrower to hit a recovering PK Thunder directly head-on will cause it to stop and force Ness into freefall. TIming can be a bit finicky but the reward is incredible.