KOA_DIO
Im only commenting on what i saw during the matches with ness.
One of the biggest things that ness loses to is shield. I did not see you shield grab him ONCE. Ness has no moves that are safe on shield(unless he spaces his F-Air). All of his aerials are easily shield grabbed. if the ness player is not fully aware of this weakness you can abuse it well.
-Try some well spaced F-tilt in this MU as well. Edit 1/8/2015 : Ness is always trying to forces his way into your space(I uses the word force because ness lacks reliable neutral tools). A well spaced f tilt could keep him out of that space.
Another big thing i noticed is that you were not properly edgeguarding ness. Often times you would just jump out at the player. You should have been able to easily cape, most of his recovery attempts. That or grabbing ledge. That at least forces the ness to recover one stage. if he's close enough you may get a Fair off.
-On DL i noticed you tried to start capping, then gave up after a few missed attempts. some of them you were not i good postion to cape, other times you tried to jump at him and cape
The biggest thing i believe got in your way was your salt. The Ness MU requires alot of patients. Ness is a punishing machine. Your began to over commit at get unnecessarily aggro. Patience is key. Edit 1/8/2015: what this MU ends up boiling down to is, how hard Ness can punish; how hard can Mario be in control in neutral.
Last thing: Don't be too afraid to fireball in this MU. i heard a little of what your opponent was saying to you. You can use Fire ball to not only disrupt his normal movement(in a way making him work around it), But to bait him/force him into certain options.
Lets say Sera approached your fireball with magnet. Most ness's would be likely to jump out at you and Fair. which you can then sheild grab.
Lets say he instead decided to just dash away and fireball. He is indirectly giving up stage position. If he commits to a grounded magnet(with aerial magnet cancels ness's do not hold
, they tap it. If they did they would be stuck in magnet longer than desired.), you can use that frame advantage to close spaces.
TLDR: be patient keep cool.