Press B, adn then run at them and press down B and than dair, they willbe at 69% so fthrow them off the platform and diar them LOLOLOL10 feet higher 

If you try this and it doesnt work, pick fox or press B again and again or press dair twice and then down B that usually works

Try to press B a lot it helps a tonn maybe press dair, bbut press B more it truly kills enemies a lto more than you think especially if they dont press L or R when they get hit

cause that means that down B doesnt work unleess you run to them, but its kk cause you can press B more. good luck and have fun.