I've decided to add a new rule to my challenge, which is in addition to doing a different language every week I'm going to try to use exclusively *languages I haven't programmed in before*.
If that's the rule, x86_64 is a stretch as I've *written* x86_64— but I count it as valid, because I've never written a whole AMD64 *program*, only snippets embedded in a C file or OllyDbg-injected into an exe at runtime. Only ASMs I've written whole programs in are MIPS and LLVM in-memory representation.