The Kirby Cousins appear in season one when Link is hack-banned by 1337f0x and sent to the DUMMY stage. They lack microphones and therefore communicate through gestures and taunts, which greatly irritates Link to the point of attacking. They come in various colours, except their cousin and apparent leader KingKirb (who is also the only one of them with a microphone).
As soon as Link loses his temper and slashes one of the cousins, he is sucked up and brought before KingKirb, who explains the reasoning behind the constant taunting of his cousins. All goes well until Link
Link and two of the Kirby cousins in the DUMMY arena.
mentions that he damaged one of the cousins in a rage, at which point KingKirb orders an attack. They are later seen pursuing Link through Hyrule Temple, accidentally K.O.'ing Lamp (causing Super64 to win the match taking place at the time).
Eventually Link is cornered and, as a last resort, tricks the cousins into taunting. With his cousins continuously spamming "hi", KingKirb is unable to hold back his own apparent urges and taunts himself, losing his crown. Vowing revenge, he orders a retreat and leaves Link alone for the rest of the series.
A Kirby cousin also appears in the collaborative "Beans", revealing Link is still an enemy of KingKirb. The Kirby sucks up Link before sending him into the portal, sending him into another universe. At the end of the collaboration, when Link returns, the cousin insults him.
It is unknown if the cousins will once again return for Smashtasm (series two).