Copy Pasta!
Thanks to everyone who voiced thoughts and concerns about the Extra Modes MVP Challenge in the comments here. We just pushed a change that reduces the number of MVPs needed to complete the Challenge from 20 to 5. (No game update is required to see the change, but you may need to restart RL if you don't see the change just yet.)
If you already have 5 or more MVPs in Extra Modes, you will need to get one more MVP in order for the Challenge to complete.