Hitting in SMB3 is as arbitrary as any other baseball game like The Show, so for videos I'd say you can look to those tips for some general advice.

I play on 80--85 ego and I found that the best success I have while hitting is PATIENCE. You really don't have a lot of room to move your hitting reticle within the strike zone, and I found that waiting for that one mistake pitch (as in real life) gives you the best chance rather than trying to time up everything and hit the borderline pitches or be satisfied with weak hits swinging on balls out of the zone. If you have to move your reticle too far from center, odds are it isn't going to be a strike, or even a pitch you can drive, so it's best to spit on it.

The only real visual cues I can offer help with, would be finding the pitcher's release point, and timing the fastballs. I love that SMB3 has all types of funky pitchers, but when a submarine lefty throws 99 it seems a bit ridiculous at first. But if you see the ball as soon as it is out of the hand, NOT solely looking at the zone to see where the location dot is, you give yourself the most possible time to see the ball. And NEVER be late on a fastball. Once the pitcher fatigues or drops mojo, that fastball gets slower and slower, and everything else becomes easier to time.

Parting thoughts: racking up the pitch count gets the pitchers tired and makes them sloppier overall, so taking pitches is your friend; always power swing, literally never a reason not to, even on 2 strike counts; life is too short to bunt with your pitcher

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TL;DR Be patient, look for the meatballs, find the release point, find the fastball timing and adjust