The Fluff, along with it's evil counterpart the Floof is a seasonal avatar. It was first released as a local species during April Fool's Day 2010. During the event, players on select main maps would run into other players to infect them with a virus. Due to demand, they were polished up and released as digos two days later.
The Fluff is usually available on the Digo Market during April Fool's Day.