Challenge Creator is a kind of activity where students can create a “challenge”, then attempt to solve challenges set by other students. But not everyone is allowed to make challenge creator activities – when I go to the page for one, the “Copy & Edit” button is greyed out with a message that the activity “uses features that aren’t publicly available”.
But can we recreate Challenge Creator using features that are publicly available? It turns out that yes, we can, sort of!
My version of Challenge Creator is implemented entirely in Computation Layer. It uses aggregate lists to store the numbers that make up each student’s challenge—in this case, the X and Y position of the point on the graph—and a Multiple Choice / Action Button combo to let students pick which challenge to attempt. (I also use aggregate lists to store each letter of each student’s name, which is unfortunately kind of slow and terrible because you need a big when letter = 1 "a" when letter = 2 "b" ... chain every time a name appears. If only aggregate supported strings…)
Anyway, this approach does have some pretty big limitations. In particular, my activity can only show 20 students’ challenges at a time, and students’ names are limited to 12 letters/spaces. It probably won’t replace Challenge Creator anytime soon 
Here’s a class code if you want to try it out: https://student.desmos.com/join/2uvcs5