It looks like they used a modified 2ndmix (again) but this time added a tricky routine where part of an encryption was running on the ARM instead of the SH as an extra hurdle to understanding.
![Image](https://sideway.re/assets/2ndmix/you_failed_game.png)
Here's one writeup from a participant:
https://sideway.re/FCSC-Quals-2ndmix-Crypto-Edition/
And a second, but this one in French:
https://redoste.xyz/2021/05/03/fr-write ... toedition/