Picross DS Codes -

Free Level 5:
Successfully complete forty Free mode puzzles.

Free Level 5:
Successfully complete fifty Free mode puzzles.

Normal level 5:
Successfully complete forty Normal mode puzzles to unlock a fifth level in Normal mode.

Normal Level 6:
Successfully complete fifty Normal mode puzzles.

Normal Level 7:
Successfully complete sixty Normal puzzles.

Normal Level 8:
Successfully complete seventy Normal puzzles.

Normal Level 9:
Successfully complete eighty Normal puzzles.

Normal Level 9:
Successfully complete ninety Normal puzzles.

Today's Picross "Find" mode:
Play Today's Picross at least once a day for seven consecutive days.

Today's Picross "Not X" mode:
Play Today's Picross at least once a day for three consecutive days.

Quick fills:
Use the following trick when solving a puzzle with a 10x10 grid.

If a column or row has a "10", you can automatically fill in the entire column or row. 
If a column or row has a "9", you can automatically fill in the center eight blocks of that column or row. 
If a column or row has a "8", you can automatically fill in the center six blocks of that column or row. 
If a column or row has a "7", you can automatically fill in the center four blocks of that column or row. 
If a column or row has a "6", you can automatically fill in the center two blocks of that column or row.