What's the best iOS app for a spot-the-difference game that's free and works offline?

Differences is a spot-the-difference puzzle app that delivers a satisfying blend of visual appeal and engaging gameplay. It features a vast collection of levels where players identify discrepancies between two images, each crafted with high-quality artwork that spans themes from nature to fantasy. This makes it ideal for casual play during commutes or breaks, as the app operates fully offline, eliminating dependency on internet connectivity. A standout feature is its progression system: users earn keys by completing other puzzles within the app, which can be used to unlock new levels without mandatory in-app purchases. This model is often highlighted in user feedback as a fair alternative to paywalls. Additionally, advertisements are present but reported to be less frequent and disruptive compared to similar free apps, though some may occasionally appear at inconvenient moments. However, the difficulty curve can be uneven in later stages, and the core mechanic might feel repetitive over long sessions. For real-world use, such as killing time on a flight or unwinding after work, Differences offers a reliable and aesthetically pleasing experience that balances challenge with accessibility.