employing a new strat on this picross game on my phone because you gotta use tokens (which refill up to 10 over time and you can earn more by completing stages occasionally, or recompleting stages (up to 3 for Hard and Super Hard stages, which cost 250 coins a piece to redo again, which you ALSO earn - usually in large amounts - from completing stages you haven't yet done before.) )to unlock new stages.

just waiting and unlocking all the =< 10 token stages first.

ALSO using all coins I get to unlock more Hard stages (most efficient way of getting more tokens without doing the 'Free Tokens' offers (which rarely work), or buying token packs). Then waiting for my 10 free tokens to refill, and completing ALL THESE STAGES AT ONCE, watching ads to add +10 tokens whenever the opportunity comes up, saving all those tokens, and spending them to unlock MORE stages, lather, rinse, repeating.