Courtyard Clash is the second Battle Course in Mario Kart: Ultra Prix. It takes place in Princess Peach's Castle, and part of the course is inside of it. Most of the course takes place in the courtyard, where Monty Moles pop out of the ground trying to hit the players. Driving on the grass will slow your kart down.
Green shells are very useful inside the castle, along with bananas and other traps. When outside the castle, tricking opponents into colliding with the jumping Monty Moles using bananas sometimes works.