I like to hang out either underneath platforms to protect me from projectiles, full hop attacks, and it lets me have the opportunity to get platform tech chases. I'd say stay grounded as much as you can, ness can get juggled soo easily and knocked offstage into an edgeguard real quick.
Ike is a hard matchup as he combos you really easily, but what I find immensely powerful is dding to low djc bair if he comes in with QD. It's frustrating because you can't straight up outrun Ike because his QD is faster than your run, and his run is almost as fast, and if you keep running, he can dash attack to catch you. It's super frustrating. So doing dd low djc bair back is really good (honestly this is an amazing tool against a lot of people, but especially ike). Just don't throw out any laggy moves like grounded pk fire because ike is like falcon where he can travel all the way to the other side of the stage in a second, AND he has a huge sword. As for snake, he shouldn't be able to catch you per se, but he can definitely limit the amount of stage you have to run away from. Not that experienced with the snake matchup so sorry. As for roy, RESPECT THE CROUCH CANCEL. Honestly you literally can't approach at all in this matchup. But if you dd correctly, grabs should destroy him. d throw can chain grab him really well, and you can pretty much do anything you want to him.
This comes to punishes. An optimal punish depends on how much lag they put themselves in. A grab is almost always a good option. I don't need to tell you how amazing d throw is lol. or even a b throw for a kill, or a f throw to set up for an edgeguard. Run up idjc dair isn't much slower, and this can also lead to so much. Also if they don't have the oppurtunity to cc, then do a low djc fair to grab or d tilt. D tilt is a truly amazing move, and it's not an optimal punish tool, but I just can't state how good this move is and even though it has pitiful range, it's actually pretty safe in neutral and can rack up about 20% on people who try to cc it, (although you'll often get hit by their d tilt anyways but whatever).
I honestly haven't found a very universal use for magdash. It's really not that good in neutral imo, although it can be good to cross up shields with. Maybe I just need to work on it, but I don't find mag dash that good in it's own right. Magnet imo should lead directly into a djc aerial, not into another mag. Mag bair is good, but pretty di, percent, and character dependent, plus it has a specific timing, so I would only do it as a combo finisher when you're very comfortable. RAR djc bair is an amazing tool for ness. I have been using it more and more lately, and it's so sexy and good. That's also a good punsih tool, and honestly it's pretty good in neutral as well if they are at high percents, cause it will beat out cc and set them into an edgeguard situation. Definitely learn how to do low djc bair OOS, and just in general to punish a semi laggy move. I end up sitting in my shield a little more than what's good for me, but it's definitely a strategy to just sit in shield at times and punish with a djc dair if they're directly over you, a djc bair if they are behind you, a djc nair if it will knock them offstage at high percents, and djc fair to regrab. Ness's instant djc aerials OOS are super good. Hope this helps!
