I was actually thinking about it, although if I do end up making them, I'll probably focus on the platformers (not much of a fan of Raving Rabbids games).
Just saw your posts in Pacman Intellivision and noticed we are currently competing in the leaderboards, I was your exact rank yesterday haha. Good luck chap :)
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Also, in RetroArch, when you run a Arcade game, you can go to RetroArch's menu and change the DIP Settings, one of these settings is the difficulty