Mr. Sun is a version of the Sun that has a face. There have been four incarnations of this character. One appears in "Procrastination." One appears in "Best Day Ever" and "Sold!" One appears in "SpongeHenge." One appears in "Sandy's Nutmare" with SpongeBob-like characteristics.
This version of Mr. Sun only has a drawn on face. It does not move or talk.
"Best Day Ever"/"Sold!"
This version is round and yellow and orange, and normally has a smile.
This version has the face of Dee Bradley Baker.
It is light yellow, and resembles SpongeBob.
Mr. Sun appears when SpongeBob looks out the window and sees children playing on a playground, with Mr. Sun in the corner. This occurred when SpongeBob was procrastinating on writing his essay.
"Best Day Ever"
Mr. Sun singing appears during SpongeBob's happy song.
Mr. Sun appeared in the sky saying "Time for work, SpongeBob" with a live action face.
Mr. Sun appears during Squidward's happy song.
Mr. Sun appeared in Shalmon's story about how a star was "Able to keep the sun and the moon happy without wearing himself out" to Sandy, SpongeBob, and Patrick Star