i'm pretty sure that for priority, it's based on the the moves hitbox disjointedness. the more a hitbox sticks out over beyond the hurtbox, the more priority it has because the larger the enemy hitbox can be with yours still connecting first.
@twilightKing: it's simple: hold down, press x then z one frame later than you would for a jc grab, l-cancel it, shine, move thumbstick horizontal (or close to it), wavedash, return control stick to down position, repeat. It involves minimal movement of the control stick (only for WDing, and moving while Drill kicking).
@LaserBust: it is kinda slow. if you want to do it faster, JC the shine (a little harder to do, and i don't think you slide as much).
Edit: i know i wanted to ask a question, but i don't remember what it was now. next time i'll ask first, then answer others.