Reharmonize a Melody
How to play
Choose a simple melody you know well, such as a nursery tune. Play it on its own, then play it with its usual chords.
Now replace one chord at a time with something different: a relative minor, a chord borrowed from the parallel key, or a chord a step away.
Listen to how each change alters the character of the melody without changing a single melody note.
Challenge
Reharmonize the whole phrase so that it sounds darker, then again so that it sounds more hopeful.
Tips
The melody notes must still belong to the new chord, or at least resolve to it soon.