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Pip_Puff
TheKenoshaKid
Don't concentrate on the flip animaition (or any animation for that matter) which you cause with the dair, instead look at the % at which you try to go for the grab. Hitstun is a function of knockback, and the hitstun animation doesn't have any effect on the length of the stun.
The stun animation is only relevant for drill rest sometimes, since the flip animation makes the victim fall on top of you and makes landing the tiny rest hitbox easier, but grab or most other moves don't have that problem anyway.
Drill grab starts (barely) working at 59%(NTSC after hit) on fox, 64% on marth, 65% on peach, 70% on captain falcon. To get the drill grab at these percentages, your execution has to be very tight. Also if the opponent di's behind you and you have to turn, % has to be higher, since turning takes 1 frame at least. Drill turn grab starts working at 67% vs fox for example.