Answers to common questions, and a real person to email if you're stuck.
No. Solo play and Battle mode both work completely offline, including in airplane mode. The only time your camera is used is to scan a friend's invite code, which happens entirely on your device.
Tap the crossed-swords icon on the home screen, then have your friend scan the invite that appears on your screen (or scan theirs). You'll both be dropped into the same puzzle and race to solve it with the fewest mistakes.
Make sure Sudoku Frenzy has Camera access under Settings → Sudoku Frenzy on your device, hold the code steady in good light, and confirm the friend's invite screen is still open (invites are generated fresh per session).
Difficulty is set when you start a new game. Head back to the home screen and start a new puzzle to switch between Easy, Medium, Hard, and Expert.
Sudoku Frenzy follows your device's system appearance automatically. Change it under your device's Settings → Display & Brightness.
No. Your in-progress puzzle, including any notes you've made, is saved on your device and will be exactly as you left it next time you open the app.
No. The app has no ads, no in-app purchases, and no subscription. It's free to play, full stop.