Prototypes are essential once we have at least one interaction (usually verbs) defined; ideally in conjunction with a core experience that the game is about.
Through this lens we can assess if the specific game play element supports the experience.

• Paper prototypes in my experience work well for meta game and strategic choices.
• Playables done in Unity, Game Maker, Construct, Phython, Unreal editor are a great way to test the physicality of real time interactions.
• Discard each prototype once it has proven the point; even if the outcome was that the idea doesn’t communicate, which is also an important conclusion.