What is the difference in the games that are listed as ...

[Rogue_Meeple]

... "Tricky", "Difficult", and "Very Difficult"?

Thanks.

[Romain672]

Tricky just add a sixth suit (and you can clue it normally, with a 'multi' color clue).
Difficult change this sixth suit by putting only one of each number on this suit. This mean, if you discard any of the card of this suit, the max score will not be possible anymore.
Very difficult make the sixth suit not cluable with their own color. Each card of that suit will react to any color. That mean, if you clue red, you will color all red and multi card. Then, if you clue blue, all multi cards colored with red will be known as multi.