Phoenix Squirrel 2015 is the subsection for sketchbook fillers starting May 2015, after a whole month when Dan didn't post any sketchbook entries. It starts with a series of milestone sketchbook entries, followed by some reward sketchbook entries, posted by Dan in an attempt to catch up on existing Patreon commissions (having removed the Patreon reward at least until he has caught up). The squirrel is presumably Dan himself, and the "phoenix" may be a reference to the initiative being a come-back analogous to a phoenix rising from the ashes.