I'll still always remember Haloid back in 2007, the best Halo + Metroid mashup video ever https://www.youtube.com/watch?v=cL-mR79GErU (re-uploaded on YouTube, it was originally on GameTrailers)
It was created by the late Monty Oum (creator of RWBY and art director for RvB) and apparently it's still the most watched video GameTrailers ever had [0]