Arduino Pro Mini

Hi everyone, last year I transformed 2 styrofoam skulls to have red blinking eyes.
My grand daughters love them. This year, I saw a project on Instructables where an Arduino Pro Mini was used with a DFPlayer to simulate thunder and lightning. My thought was COOL! Add this to the Halloween stuff! So now I am knee deep into it and again finding difficulty with Arduino and IDE. Figuring it out (I think) a step at a time. AH HA! Just got blink to work on the Pro Mini! All without errors while programming! Yay! Now to figure out why so many errors with the sketch provided on Instructables...