Nintendo today advised that Super Mario Maker will soon receive a free Mario & Luigi: Paper Jam Bros. update, providing access to a Mario, Luigi and Paper Mario costume.
From 3 December, those who beat the Paper Jam Bros.-inspired Event Course in Super Mario Maker will receive the costume.
— Nintendo of Europe (@NintendoEurope) December 1, 2015
You can get to the course by heading to Course World > Event Courses.
Mario & Luigi: Paper Jam Bros. heads to the 3DS on 10 December. We reviewed Super Mario Maker here.