against peach you're lucky that you weren't CC down smashed for more nairs than you were. you can try using dair and up air instead of just nair. they put the other person in different positions which may be better for you in certain scenarios. i don't know why you decided to quick attack down and up twice when you were in the same position that you were when peach managed to punish you for doing that before. forward smash isn't that great of a move. sometimes it has utility but you'll rarely land the final hit because it will either be SDi'd by the opponent or you'll be aiming to time the final hit, which is really hard and not applicable often. you went for a lot of up smashes that were a bit too ambitious in my opinion (mainly in the yoshi match, but peach too). it looked like you were hoping that the other person would jump into it, which happened, but this strategy won't work once you're playing against more experienced people who won't automatically make errors in neutral consistently enough. the other person also wasn't being tricky with how he was approaching, which is something you could've handled a lot better. when you shield, wavedash back is a decent option since it gives you space and the lag from the wavedash can't be reacted to by the opponent. i thought i'd tell you this since i saw you grab OoS against peach, resulting in her punishing you. nair OoS is also 1 frame faster than grab if you do it perfectly.
i liked what you stringed together with the nair > down tilt > nair even if it didn't quite work out. that bair you landed after escaping peach's dair (idk if you smash DI'd it, but that doesn't matter).if you want guaranteed damage off a throw, up throw up air is true against the whole cast at varying ranges. if you're going to down throw, you can pummel and buffer the throw with the c stick. this only works with down throw, jsyk. i'm fairly sure down throw never leads into anything guaranteed, though this may not be the case with peach and yoshi since their double jumps dip down before rising. that said, there's nothing stopping you from doing something like down throw > shield/dash dance away to bait an aerial and then regrabbing or doing whatever you want.
edit: it's nice that you tried to use agility tech but it's pointless 99% of the time. dash will take you wherever you want to be on the ground much faster.
