Mary, Did You Know by Clay Aiken is in Abm at 50 beats per minute and runs 2:43 across 22 bars. It uses 13 chords — Ebm, Db, Abm, Bb7sus4, Bb7, Abm7, Gb, Bbm, and a few more. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? Mary, Did You Know guitar melody tab.