I'm making a video game, and thought of making a boss theme, where I use an 8bit remix and the original instrumentals of the song Chop Suey. I'm already in contact with the 8bit versions creator, but I'm not sure if I can use the original instrumental, without my game being taken down.
You need permission to use the work in your game. Just because a work (like a song) is freely available for you to play/use does not mean that also have the right to re-distribute the work yourself. You need to specifically seceure the right to use the work in your game from the person or entity that holds the intellectual property rights.
Music in particular is interesting, as both the composition and the performance are subject to intellectual property laws. You generally need to secure the rights from both parties (if they differ), in order to use an existing recording of the song.