EPQ stands for Elevate Proficiency Quotient. A proficiency quotient tracks your performance. EPQ ranges from 0-5000 and is based on game performance, consistent training, and game variety. EPQ can increase, decrease, or stay the same depending on how your game scores compare to your historic performance and frequency of play. EPQ is not just based on the individual game but on all games in the same category (all games in the Writing category for example).
Difficulty determines how challenging a game is based on your level of gameplay. When you take the onboarding test, you start at a difficulty level set by your test results, which adapts as you progress to ensure your experience is challenging. Difficulty levels range from 0-400 for each game. If you're at a 400 difficulty level for a specific game, you'll still get new content and continue to earn EPQ.