Sanderson is now the ruler of Pixie World, following Durante's original laws more than H.P.'s. He calmed down almost completely after H.P.'s death (but still has random Pixie spaz moments). He's somehow dating Princess Bubblegum while dating Shelly while dating three other girls at the same time, but that probably isn't canon.
He was adopted at a very young age by H.P., after his biological parents died.
Sanderson has three floofs on his hair as bangs (two in canon), resembling the crest of a Cockatoo. Like all Pixies, he can flatten them and raise them, but has trouble keeping them flat. He was a scrawny twig at a younger age, but has currently filled out to a normal male Pixie structure. He wears a normal grey Pixie suit with H.P.'s hat.