Don't panic. You can do this. When words like "muscle-up" show up in the WOD, people have a tendency to freak out. Don't worry about it. Just like everything else, there's a modification. If you can't do a bar muscle-up, it's OK, you can do chest-to-bar-pull-ups. Don't have those? Use a band or some other form of assisted pull-up or row. Or if you're just learning bar MU's and can't do the prescribed amount, trying doing a lesser amount. It still works. DON'T FREAK OUT!