Notes:

I don't think this counts as a crossover since it doesn't involve any specific scenes or memes from other media, and none of the characters interact with others outside of their series. Except for the Doom X Pizza Tower one, but that's one out of like, 30. And Lancer dressed as Cartman. And Modeus and Soldier telporting bread.
Also I don't know about a quarter of these characters and series, so please feel free to point out tags I miss.