What that guy said is wrong, Blizzard isn't a good punish for dair. It's a decent punish against Mach Tornado though. You aren't doing anything wrong that makes them able to dair you halfway through it, that happens to everyone if they are mashing dair.
D-Smash ISN'T safe on first hit, remember? We had that discussion about 15 posts back. Just power shield it and grab him.
-LzR-, if you KNOW what he's going to do in a situation, you can punish it.
****, I've punished d-smash before with SH f-air. (Might have been full hop, but I'm almost certain it was SH.) It goes right under you, and then you get a tech chase from the fair.
You want a list of things that can punish d-smash on a read?
Read him d-smashing (this only applies to first hit)
space yourself to make him whiff, walk in f-tilt
space yourself to make him whiff, walk in d-tilt
power shield, dash upsmash
in fact, power shield -> any grounded move besides belay
SH blizz/fair/nair/dair
RAR SH bair
Blizzard out ranges it
bait it, IB chaser.
What more do you want from me.