The LEGO Day marathon was an 14-hour marathon event that occurred on Cartoon Network on December 13, 2015, from 6AM to 8PM. As the title implies, Cartoon Network aired nothing except LEGO programs all day, including the Mixels special "A Quest for the Lost Mixamajig." The event was made to promote the sneak peek of Nexo Knights that aired that day.
- 6:00AM - LEGO Mixels: A Quest for the Lost Mixamajig
- 6:30AM–3:00PM - LEGO Ninjago: Masters of Spinjitzu marathon
- 3:00PM–3:30PM - LEGO Scooby-Doo! Knight Time Terror
- 3:30PM–4:00PM - LEGO DC Super Heroes: Batman Be-Leaguered
- 5:00PM–6:00PM - LEGO DC Super Heroes: Justice League - Attack of the Legion of Doom (NETWORK PREMIERE)
- 6:00PM–7:00PM - LEGO DC Super Heroes: Justice League vs. Bizarro League (NETWORK PREMIERE)
- 7:00PM–8:00PM - LEGO Nexo Knights: The Book of Monsters - Part 1 and Part 2