The Guild of Sidekicks is made up of sidekicks of well known heroes, as Crow is to April Ryan. It is presumably related to other Marcurian guilds such as the Guild of Merchants and the Guild of Tourism. The Guild awards a badge for the 'Sidekick of the Month' which Crow was presented with after the events of TLJ, although he lost his mantle the month after that to a suspiciously familiar-sounding sidekick, much to his annoyance: "... that annoying man-child with the hairy feet and the chubby face got the badge. What did he do? Carry someone up a hill? He didn't even crack a single joke to lighten the mood! No sense of humour whatsoever."
According to Crow, a sidekick's credentials involve banter and commentary, giving helpful hints and fetching and carrying, as well as the occasional "inappropriate joke". If we take his comments from The Longest Journey too, sidekicks are also very resilient: "Honey, I'm the sidekick. Didn't you ever read any legends? The sidekick always survives!"