While games like Fortnite and Dead by Daylight have pushed them to the forefront of the gaming industry, crossovers have been a part of the video game landscape for decades. From 1990's Alex Kidd in Shinobi World, to 1993's Battletoads and Double Dragon crossover, to the prolific Marvel Vs. Capcom series, video game crossovers have been around for a long time, and for a franchise as big as Halo, it's only natural that the Sci-Fi shooter has seen its own fair share of collaborations over the years.