Hmm. I’ve been seeing a lot of your posts around the forum lately, and the one problem I keep hearing about is getting that one hit on your opponent. Magneto is excellent at that, you may want to keep at it. No advanced combos for the moment, just basic Magnetic Blast stuff or fly loops could work. Focus for the time being, however, on getting your different tridash approaches down. Sentinel Drones is an excellent assist to cover your ass with as it just takes up so much goddamn space and puts you in so much blockstun. Make sure the opponent blocks the drones by trying to zone him into staying on the ground, with Disruptahs, Magnetic Blasts, and Attraction/Repulsion/Gravitation. Once they block drones, you can move in and tridash like hell and it’ll be safe. Basically you can go for tridash j.L, empty tridash c.L, or empty tridash throw. Also practice crossing up with tridashes, 'cause drones aren’t a true block string IIRC so you can mix them up in the small window between one drone and the next. Magneto can cross-up empty tridash into c.L, but you can also tridash with a superjump so that you can come down with j.M or j.H, both of which can hit behind Magneto. If they block successfully, just tridash again, this time with a new approach (mix it up; don’t be predictable by just going high-high-high or high-low-high every time). Drones assist takes enough time that you can do, like, 3 tridash mixups in a row, I guess.
Drones pressure isn’t gonna cut it though if the opponent stays in the air for the majority of the time to evade it. That’s okay, Magneto can still convert from air hits. Doom Missiles helps control the air. It can catch the opponent pressing buttons and you can easily convert with j.H xx Magnetic Blast or j.H j.S xx ADDF j.H or j.M j.H xx Magnetic Blast or a combination of those if the opponent does get hit by Missiles at super- or normal-jump height. Be unpredictable with your air throws. You can wavedash then jump then immediately air throw to punish some slow-ass move the opponent uses from around midrange. Scoop the opponent off his air dashes, scoop the opponent off the recovery of his air moves, scoop the opponent off the startup of his air moves, whatever. Just make sure you get the air throw and you don’t get hit. Magneto is pretty quick to move around the screen to get that air throw, but you’re still gonna have to eyeball that shit to know if a certain move is gonna outstart you or not. That just comes with matchup experience.
Now, Doom and Sentinel are great assists, but they have slow startup so you can’t just call them when your opponent forces you into the defensive. Judging from some of your posts around the site, you also seem to have a problem with defense. One thing you have to keep in mind is to stay safe. You can’t just push-block then Disruptah and hope for the best, even if a lot of the time that works. You have to watch how your opponent tries to approach you. If you’re going up against, say, Nova, he’s just gonna box dash j.H that Disruptah and kill you. Chicken blocking (up-back) gets you out of some of the nasty shit, but you’re still prone to left-right mixups. Just work on your blocking, wait until the other guy does something unsafe, and take that chance to either punish him or get the hell out of there. It’s usually better to punish unsafe moves, but if you’re unsure, that window could be used to sort of reset the neutral so you can get back to fishing for hits with Missiles and Drones. Punishing takes time to learn as well; it relies on matchup knowledge, knowing what to punish and what not to punish, but that comes naturally over time. Holes in the offense are not always so easily seen. Sometimes you can easily see that something is punishable, like Nova ending a blockstring in c.M or Deadpool with a Shoryuken (standing S), but sometimes it’s something hard to see, like Wolverine’s Berserker Slash or Vergil’s Rapid Slash. People have already figured out that those moves can be jabbed or thrown out of during startup, but Wolvies and Vergils still sometimes do them raw, and I can imagine people still doing them online. Learn how to punish that kind of shit, don’t just let them put you into blockstun all the time, especially when they use such unsafe moves to do it. There are also times when you have to realize that you just have to block for a good 5 or so seconds before an opening comes up, like Vergil Swords bullshit. These are the times when you just have to block, but don’t sleep on it though, when the opportunity to go on the offensive comes, by all means take it.