Ness's English crowd cheer is a reference to the Super Nintendo Entertainment System, officially abbreviated as the Super NES or SNES, which itself is a reference to the fact that Ness's name is an anagram of SNES, and the "NES" part is often pronounced "ness".
A glitch occurs in the 3DS version, seemingly caused by entering a battle as Dr. Mario on one team with three Villagers on another, on Yoshi's Island. The glitch causes the crowd to chant "Popo! Nana!" the names of the two Ice Climbers, even though they aren't in SSB4.