An aerial Double shine can be fast enough to hit an opponent who DIs in twice.
Due to knockback stacking, this sends the opponent at the 'true' shine angle; that is, zero. A single aerial shine, on the other hand, sends at an ever-changing, unpredictable angle because they have existing knockback.
“ Combo into aerial double shine aka the Zuppy shine is an optimization on the usual comboing into single shine. They can escape by DI/SDIing away but then the shine is more lethal! ”
— cookbook.gg