I'm actually the guy (Sam) from that post! Never got DOOM running on the Furby, but I was able to get a custom version of Pong running, with accelerometer controlled paddles.
The CPUs are definitely weird, and I ended up porting Ghidra to support u'nSP as part of that project. https://github.com/SamuelWAnderson45/sleigh-unsp Reverse engineering a CPU was a wildly fun learning experience; still proud of that project.
Can you share any more details about the Pong port? I have been collecting various bits of information about u'nSP processors, particularly the SPG2xx series used in mid 2000s plug-and-play games, but so far I have never seen an actual homebrew game for any of these chips (with the exception of the Mattel Hyperscan's SPG293, which however uses a different architecture).
I have also been looking into the newer GeneralPlus GPM4x30 SoCs used by some modern Chinese plug-and-plays with HDMI output, at least by the ones that aren't straight up Famiclones hardwired to a composite to HDMI upscaler. Those are ARM based so much less of a pain to reverse engineer but also much less fun...
The CPUs are definitely weird, and I ended up porting Ghidra to support u'nSP as part of that project. https://github.com/SamuelWAnderson45/sleigh-unsp Reverse engineering a CPU was a wildly fun learning experience; still proud of that project.