Speaking of TCGs

If nerds like cards so much, why aren't books printed on cards? That way, putting them together in the right order is a fun puzzle, plus you can charge them a thousand times for a short novel.

Unbeatable Idea for the Next Magic: The Gathering Set

Harry Potter.

Unbeatable Idea for the Next Yu-Gi-Oh Archetype

Summer Skull. Think about it. More importantly, think about a mobile game that isn't a simulator, and also it's a crossover game with every trading card game, and it's a gacha. Tower defense? Maybe.