I hope these things hasn't already been suggested for Yoshi...
His Neutral Special could have the option to slightly angle with the Control Stick/Pad before Yoshi sticks his tongue out. And if needed, the range and/or damage could be reduced to help balance out the ability to angle. But I assume even with those changes, the ability to angle would still be unbalanced for Yoshi. The same could also be done for his Grab, but that would be blowing balance out the window.
For his Down Special, he should also have the Jump Cancel buff that was given to Bowser's Down Special. Though the height of his Flutter Jump might cause balance issues. Also keep the launching hit that was given to this move in Brawl. But if the Jump Cancel does get added to this move, that could also cause balance problems...
For his Side Special, remove the disabled fall when the move ends in the air. And instead, make him unable to use the move again until he lands on the ground. The turning speed could also be slightly increased. He could also have the ability to accelerate faster, deal slightly more damage, but have less control the longer he rolls in the egg, but the buffs are removed if he reverses his direction.
For his Up Special, keep the distance gained when used in the air that Brawl has. That was a great buff in my opinion.
For his Final Smash, he should have the option to only spit the Fireball when the Attack Button (A Button) is pressed, and to spew his flames when the Special Button (B Button) is pressed.