It doesn't work any % on any character. Dtilt has 3 different hitboxes: the first (the one closest to Lucas) sends your opponent at about a 75° angle, second (middle of dtilt) at about a 40° angle , and the third (tip of dtilt) hits them horizontally (361°). The one closest to Lucas deals the most amount of hitstun and sends your opponent at an angle such that is very difficult to get out of.
Against fast fallers (
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;
;
;
;etc) the dtitl will not launch them high enough for any real follow up before they can reach the ground and roll/shield/spotdodge before about 50%.
Dtilt's never really going to true combo into grab but the combo challenges human reaction speeds (you have about 12 frames of hitstun, 13 frames average reaction time, and 6-7frames of input lag so reacting to the hit can be tough).