For getting 3 stars on puyo adventure levels, usually the hardest are the score based ones since the AI can just die before you have enough time to build up score. The best bet is probably taking your time to build up a single larger chain. A 5 chain or so should be enough to net you 3 stars right away. For time based ones you can usually just make it by playing quickly even if it means spamming smaller chains, the AI isn't very good at clearing the trash quickly.

You can add me if you still need online achievements

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