Well, it's going to end with a bang, team. 20.5 is a pretty unique workout and any way you slice it, it's going to be a good challenge.
Ring Muscle ups and pullups form the Rx and Scaled gymnastics portion, along with rowing for calories and wallballs.
The interesting part is that you can partition the reps for the exercises however you like, which can lead to many possible different versions of the workout. What version you come up with will be largely based on your skillset, so chat with your coach about a strategy around getting the most work done!
The full wod is this:
Warm-up: 5 minutes of Cindy (5 pullups/ring rows, 10 pushups, 15 squats) - at a SLOW pace!
FOR TIME (with a 20 min time cap):
Rx: 40 ring muscle ups, 80 calories of rowing, 120 wallballs (14/20)
Scaled: 40 pullups, 80 calories of rowing, 120 wallballs (10/14)
Now if you don't have your pullups or muscle ups, this is a RACE to finish the rowing and wallballs - as there will be a tie break time once both of those are done.
If you might get SOME ring muscle ups or pullups, try to get them in the first 4-5 minutes of the workout then get after the wallballs and rowing to make sure you get that done also.
If you're stronger at pullups or ring muscle ups, consider doing rounds of all three movements (i.e. 5 pullups - 10 calories rowing - 15 wallballs x 8 rounds). If you do this, YOU MUST HAVE VERY FAST TRANSITIONS, as you will be switching a lot between each exercises.
One tip to minimize transition time is to not strap your feet fully into the rowing machine - have the straps tight enough that you can pull yourself back forwards but not so tight that you can't get in and out quickly!
The video below highlights these points and more: