dthrow dair took some getting used to, its basically a fox short hop and during a grab you aren't used to having to do so many things at once, you will get it down though and it will become second nature, what sucks is when people start learning how to get out of it, it pwns people who don't have enough experience vs Ice Climbers.
VS Peach I like to platform camp and try to catch her pulling a turnip, to defeat peach you have to have to predict them a lot. First of all never just wavedash in vs a decent peach because they can slap you away with a double jab dsmash you, or just fair in place to block approaches. What you need to do is get in positions where you can catch her during aerials with fairs and nairs. Watch for when they like to dsmash and fair them, then you can immediately dsmash her or chase her roll/getup because the fair should spike her into the floor (the peach would be crouch canceling). If you do approach with a wavedash space it well and do it sparingly and up angled ftilt should beat most of her options and if you spaced it well she won't be able to hit you after she cc's it. If you stay close enough and predict when she is going to throw a turnip you can nair her, also I like to nair with the z button when she has a turnip at close range, if she throws it I have a good chance at catching it and hitting her. Peach is slow she can have trouble chasing your rolls, its a little safer to use them vs her that other characters and often times its better than light shielding because her attacks eat shields up so fast, ITS VERY IMPORTANT that you keep your shield healthy because she has a lot of moves that shield poke and pressure and attacks that separate our climbers.
Lastly peach has a lot of moves that aren't really punishable, IE any float canceled aerial, and her jab, there are a lot of times where a dash attack or dsmash look punishable but aren't, practice is key in this match, look for her openings and keep on the pressure, 99% of your kills are gonna come from grab upsmash, good peaches won't let you just hit them with random ones. You should counter pick levels with small sides and ceilings. I personally like Yoshi's because a grab there can lead to stocks early and it gives peach less room to turnip camp you in any form.
