So... mystery chords... What is a mystery chord?
Have you ever fiddled around on your guitar, and come up with a guitar chord that sounds really good, but because you literally just created it by ear, you have NO idea what to call it, let alone how to use it? (Side note - you can use my guitar chord tool to reverse-engineer your guitar chords)
That's a mystery chord.
I've even seen pro musicians refer to their own little mystery chords... For instance, heard Danny Gatton say something like this one time:
"here's this little thing I came up with... it works in E"
As you've heard me say before, guitar theory simply explains what sounds good to our ears.
So, that's what we use to explain what those chords are.
There are many, many weird and wonderful chords, but there are only 4 main varieties that account for the bulk of the chords you'll see out there.
In my Guitar Theory Crash Course (Unlocking I IV V), I go into detail how to build each of those chords.
Once you know how to build them, you also know how to recognize them.
And once you know what to call it, you'll know how to use it - or at least you will if you've taken my I IV V course! (Because I teach all that stuff in there).