Magnet stalling, DJC pk fire when appropriate, bat. To be honest it can be rough to get in on the belmonts and they have some of the best ledgetrapping tools in the game. You can try and catch holy water if they ever use it in neutral, but thats doubtful however. You have to read their tendencies, if they up b out of shield often when pressured its an easy punish. If they dtilt, you can try and parry the second hit. It can be rough, but it goes both ways. When you do get an opportunity abuse their poor recovery options, with yoyo, pk thunder gimps, and fall down nair. They also have a hard time coming down, continue to pressure with upairs and pk thunder. I have also included some sets with Ness players in the matchup and hopefully that gives you some insight as well. Good luck!
https://www.youtube.com/watch?v=Bo6smQQRFQ0
https://www.youtube.com/watch?v=gUqQBwnjzxU&t=7s
https://www.youtube.com/watch?v=6W7UEF2r5wU
https://youtu.be/ec3t7xnoHMo