For the weeks of Black Friday and Cyber Monday, GameStop is having a series of different "Buy X, Get Y" sales for certain older consoles. This happens to include the DS and newer including the Wii and Wii U. The sales are for pre-owned (used) games which might or might not be complete. They are along the lines of, "Buy two, get two free on games $19.99 or less," or, "Buy four games priced $14.99 or less for only $30."

Some I found include:

Buy Any 4 Pre-owned Games $14.99 & Under for $30!
Save Extra 15% on $100. Buy 2 Get 2 Free on $19.99 & Under Pre-Owned Games!
Buy More Save More! Save 15% When Buying $100 or More on Pre-Owned Software $19.99 and Under!
Buy any new title $29.99+ and get 30% off 1 pre-owned title, or buy any 2 new titles $29.99+ and get 50% off 1 pre-owned title!
Here are some examples of what games are included:

I hope this helps!