Ghost Ian is one of the ghosts that appear in Epic Mickey and in its sequel. Like Gremlin Prescott, in the first game Ian appears as a minor character, but in the second game he plays amuch bigger role.
In Epic Mickey
In the first game, Ian was one of the many ghosts that had to move out from Lonesome Manor to Bog Easy when the Pipe Organ went crazy. Before Ian and all the other ghosts moved out from their home, one of Madame Leona's books flied out of her library to Bog Easy and she blamed Ian for it. So the player has to recover the book for Ian and return it to Leona.
If you find Louis's courage medal in the Sunken Steamer, Ian will try to buy it from you for 200 E-Tickets.
In Epic Mickey 2: The Power of Two
In the sequel, Ian acts as the "self-appointed caretaker of Blot Alley and the Spatters" (described by Gremlin Gus). You first meet him when entering Blot Alley, then he explains that he dosen't see a lot of Toons because of their fear to get chewed on followed by his slow progress in making the Spatters friendly.
Ian can either help the player or difficult him the progress through the game depending on how you treat the Blotlings in Blot Alley and Fort Wasteland. If you befriend the Spatters in Blot Alley, he'll open the gate to Club 13 for you and give you the Spatter Whisperer Pin.
In Fort Wasteland, if you befriend the Spatters and Deloris the Slobber, he'll open the projector screen to the Floatyard and give you a Flower costume. If the Blotlings are thinned, he won't open the projector screen, but the archaeologists will open you the D.E.C to the Floatyard; also Ian will summon five more Spatters and give the flower costume but in some bad shape that you will have to pay the haberdasher 150 E-Tickets to repair it.
Ian (if you choose the bad path), along with Deloris the Slobber, could techinally be mini bosses of Fort Wasteland.
In the good Ending he will be giving Ice Cream cones to a pair of Spatters, while Deloris will be offering an Ice Cream cone to Paulie. In the Bad Ending, the Spatters will be throwing Ice Cream to some Toons and Ian.