With the server shutdown this achievement is now unobtainable.
The other guides are great, but this is mainly for the people that have more than 10 remixes and still don't have the achievement. If you have that problem then skip to the bottom. The first part is to explain for anyone just starting.Creating the remixes
First of all, this is best done with a second account (Gold or Silver membership) or a friend that is online at the same time you can communicate with. Have your friend/second account find the world you want remixed and click "Remix." From there follow the below:
3. Save + Share
4. Place in a new slot
5. Make it Visible to all
6. Exit the world
Repeat the process until there are 10 remixed worlds uploaded at the same time. Log in to your main account, or restart the game when your friend says they've done it, and the servers should update and pop the achievement. If not, refer to the below section.Fixing the remix glitch
I only found this because I had 25 remixed worlds active and only 10% progress. The tracker will only improve if the lineage tab has your world with the creator or co-creator label on it. In my case, the lineage glitched and said "UGC Error." I could earn rewards from the remix, but not the achievement. Just verify that all worlds that are remixed have your account as the next world in the lineage chain and it should pop without a problem. If you find a world that results in the UGC error when remixed, then remix another world on your main account and try it with that one.
Out of courtesy, delete these remixes when you're done so you don't clutter up the feed for those trying to get Rising Star or also want Catalyst. It's also a good way to have your upload privileges revoked, if Team Dakota still enforces that.
If this fixed your progress please leave a comment! I want to make sure this works for people. Hopefully it helps someone.