Quick notes:
- You're not optimizing your combos. If you connect with a fair, and your opponent doesn't SDI, you have a lot of follow up options. It seems that every time you went for uair. All that does is put Marth above you, while you slowly descend back to stage. Alternatively, consider doing something like fair>magnet>nair or fair>magnet turnaround>bair to put Marth offstage and in a position to for you to edge guard.
- You're allowing him to return to stage for free. I know that you already acknowledged that you tossed out too many PK Flashes, but here's why it's bad. Marth is hard enough to get something started on when you're on an equal playing field. You need to make the most of your opportunities. Ledge drop rising nair into immediate dair is a decent option, down smash if he fails to sweet spot, jump off magnet>nair is also good. You have a lot of options here, it's just catching him before he can hit you with the disjoint that's hard.
- You're recovering way too close to the stage. Any experienced Marth is going to jump up and dair you out of your charge animation. It's easy to react to. Also, recovering low, Marth can just ledge hop dair you. It's a sad life. Fade back, recover high, when he inevitably fairs you, DI out or weave to try and get tipped so you pop up and can drift back without using PKT.
- You're too aggressive. Ness is a bait and punish character even if his design seems to say otherwise. His shield pressure isn't the greatest, and Marth is just going to grab you or dtilt you out of everything. Dial it back, dash dance more, wait for more openings before going in blind.
It's obvious this player wasn't experienced in the MU, so you played fine in that regard. But if you come across a more experienced Marth player like JReed, Sora, or Emukiller, you're going to have a much harder time.
Overall, your Ness is technically solid. You know how to control the character. Seems like you just need more game experience, which will come in time.
Keep it up.
