In other words, you want a password that doesn't just contain one "class" of characters. Then you can use
^(?![a-z]*$)(?![A-Z]*$)(?!\d*$)(?!\p{P}*$)(?![^a-zA-Z\d\p{P}]*$).{6,}$
Explanation:
^ # Start of string
(?![a-z]*$) # Assert that it doesn't just contain lowercase alphas
(?![A-Z]*$) # Assert that it doesn't just contain uppercase alphas
(?!\d*$) # Assert that it doesn't just contain digits
(?!\p{P}*$) # Assert that it doesn't just contain punctuation
(?![^a-zA-Z\d\p{P}]*$) # or the inverse of the above
.{6,} # Match at least six characters
$ # End of string