When a tipper uses his wild card he gets double the points for that round.
eg if I picked 6 winners AND I used my wilcard then I would get 12 points.
The number of wild cards that a tipper can use in the ENTIRE season is determined by the administrator.
It is set in the competition preferences.
You don't have to use wild cards in your comp if you don't want to, but they can make things a bit interesting.
It is up to the tipper to decide when they want to use a wild card.