In
The House That Gave Sucky Treats, if you gave Strong Bad the marshmallow peep, he put you on his "People I Gotta Egg Today" list. Kewpie Dan was one of the other people on the list.
Clicking on his name brought up a picture of him in a new window with the title "Get FushLing!" I'm not particularly sure what that means.
Debut:
The House That Gave Sucky Treats