Based on the fictional retro arcade game featured in the 2012 Disney animated film Wreck-It Ralph, Fix-It Felix Jr. draws inspiration from Donkey Kong and other arcade classics in its defictionalized arcade cabinet.
After having his stump moved by a construction company, Wreck-It Ralph seeks revenge by damaging the apartment building built on his land. The citizens of Niceland call on Fix-It Felix Jr. and his magic hammer to repair the damage Ralph is dishing out and force him off the building, the player climbing from ground level to the roof in each new level. Levels are made up of multiple screens where shattered windows must be repaired by swinging Felix's hammer, the player moving up to the next layer after all damage on the current screen has been repaired.
While hopping from windowsill to windowsill to repair the glass, Felix will be bombarded by bricks from above as Ralph continues his demolition. Being hit by a brick will make Felix lose a life, and in later levels passing ducks can also damage Felix on contact. Ledges are added to later prevent the player from jumping vertically between certain windowsills and clumps of bricks will sometimes drop to block horizontal jumping as well. Felix can also pick up pies left by Nicelanders to turn invincible for a time.
Fix-It Felix Jr. generates new platforming levels endlessly rather than looping, introduced hazards still appearing as players push into further levels.