The easiest way is to play 15 brawls on Shadow Moses Island. Just set it to 1 stock and break down the walls, then run off. Do it 15 times. Bam. Snake challenges.
Easier way is to play stamina with 1 hp on the computers and any number higher than theirs as yours and play with the poson flowers as automatic ocnditions and you win every match. TAAAAAA-DAAAAAA