Noel gift for your friends!
ARDUINO BOARD (In my case, it's UNO R3)
Dot Matrix Display (I used 5x7 red one)
Note: I additionally used Li-Po battery and Adafruit POWERBOOST 1000 to make that thing working without any power cable.
As given in code, column pins goes Arduino's Digital 2-6 pins and rows goes to 7-13.
You can use cheap chineese powerbank instead of Adafruit's POWERBOOST thing.
Multiplexer is more useful and educational for you, using 12 Digital pin for one component does not make sense.
I used the website http://dotmatrixtool.com/ fill the blanks and click generate button.
Status of the boxes in website might be different to light a led, depends on your dot matrix's type. (anode or kathode) some of them lights on "1" bit, some of lights on "0".