Part of my training is watching match vids of my mains involved in various MUs. As someone who's often in FG Teams and loves team matches in general, I download replays from the Share section and focus on FG (the 1st & most common place I check), plain ol' Team Smash (I'll admit, it's rather hard to find matches w/OUT CPUs involved), and then FF Teams (honestly, I've not been looking there for ages) featuring my mains or secondaries or anyone else I'm curious about. I also start looking within the U.S. region and then the World. I even tune in to Spectate and the Replay Channel occasionally, hoping to find a GOOD player like Cutza & Six for Jr. There's actual tournament matches over at YouTube and Twitch and other places that I'll search for, with VGBootCamp being one of the absolute biggest names in streaming competitive Smash. I definitely try to find tournament matches with actual commentators (bonus points if they're in the know about the MUs at hand), team battles in particular (any big 4v4 tournament matches that have happened recently?
![Stick Out Tongue :p :p](/styles/default/xenforo/smilies/tongue.gif)
). AceStarThe3rd's Undefeatable series is highly recommended viewing material as well.
As for Training Mode-- or rather, the Combo Labs as I refer to it as, it's definitely THEE place to go to try out various ideas, tactics, approaches, etc. Whole characters can be picked up here. It's also where I found out quite a number of things, like how both Jr's Mechakoopas & Cannonballs (default versions, as far as I'm aware) can challenge ALL of DH's projectiles, as well as Jr's Side B Jump Cancels & its numerous applications, and how DH can both produce many projectiles that can stuff other projectiles AND be mobile with/away from them, among others (ex. answering Flare Blitz spam with Alph, Pac-Man, DH, Jr, the question of who can duck, crawl, and DTilt under Thoron, and more).
I definitely frequent FG Teams most of all, once I'm done contributing points to whoever's in the Conquest at any given moment (as of this post at this point in time, it's Kirby) in FG FFA, since points are valued by the amount of KOs you rack up, as well as how high you place in the match. With 3 other players all against you for 2 minutes, it's a KO goldmine.
As of late, I've been trying to contribute match vids for the Share section of both the 3DS and Wii U versions for FG Teams, most notably for characters that hardly have any footage for them, like G&W, Alph, WFT, Falco, Char, Zelda, and of course my mains, Jr & DH. If you find Sploosh with "OpenDEAL! MICRO!" & Saki Amamiya's face in the profile, that's me.
Earlier in Smash 4's release, when I wasn't comfortable with certain characters in a team environment, I went to For Fun Teams and threw myself in the fray. I considered myself ready for the big leagues that I consider to be FG Teams (for now) with said characters if I can win 2 out of 3 matches there, which I did. Among the last that I have done so were Metaknight & Palutena.
Research is also a part of my training. I definitely look at frame data for various characters, especially my mains, which the Competitive Discussion area of our awesome forums have posted. Said frame data revealed precious intel that have helped me find some new characters to rep for certain MUs, most notably Falco of all people. He's apparently the lowest tiered character to EVER have been blessed with a 2-frame Jab like 3S!Chun-Li's Crouching LP. O_O Not even YOSHI has anything like that, just 3 frames on his Jab & NAir at most.
I definitely agree with GanonPawnch's advice. Sticking around in a room that feature players that either body you and/or use characters that body your characters is a great way to improve and grind out MUs, including potential counterpicks. I care not about my records, even though I occasionally check them from time to time out of sheer curiousity. I tell you right now, a bunch of my losses came from grinding out MUs that are bad for my mains Jr & DH, like Yoshi, Sonic, Rosalina, and more.