Help with Flappy Bird Sketch
The arrays need to be tagged with the keyword const.  It is possible that the original sketch was written using an earlier version of the IDE that you are using (or a later version?) and your version requires the const keyword whereas the author's doesn't.

Basically any arrays that are PROGMEM need the word const adding to them.  For instance, lines that start:

static unsigned char PROGMEM ...


need changing to:

static const unsigned char PROGMEM ...