What inspired the topic this time are two things. First is one that was a very pleasant surprise is Ziggurat, the company that owns the rights to the Slave Zero IP, recently worked with a Quake modding group to create an officially sanctioned Quake Remastered mod based in the Slave Zero universe that also helps act as promotion for Slave Zero X (a 2D prequel to the 3D third person shooter from 1999), and the second is dataminers have discovered evidence a crossover with Warhammer 40K is likely coming to Call of Duty Warzone and MW3 soon as load screens depicting Dark Angels and Adeptas Sororitas were discovered in the game files.
One that I personally really liked just because of how amusingly goofy it was is there was a period of time Metal Gear Solid and Ape Escape did crossovers in the third games in both series. MGS3 Subsistence had a game mode involving Snake needing to capture apes, and Ape Escape 3 had a game mode involving an ape dressed like Solid Snake needing to infiltrate an area.