This is unlocked by being in Rank 100 and also completing ALL THE TRACKS by winning ALL GOLD MEDALS AND EVEN THE BRONZE AND SILVER with the exeption of Intelligence Town Monkey.
There are 5 Starts and One End.
The starts come from the rays and going to center. You can place towers on the yellow parts. The stars are the size of a Dart Monkey so,you can only place dart monkey sized towers there. There isn't much space for the towers.
Monkey Apprentices are 66% more powerful. When you have 60 Monkey Apprentices and 60,000 money, a message will appear and says: Do you want to activate the Star Rays? Click Yes and Star rays will be everywhere!
The Star Rays will last up to 10 rounds.
When you earn all the medals for all tracks and all missions or 1000 Daily Challenges, everything will be your "Overall Extremely the Champion of the whole Blooniverse Medal" The Bloon Globe, it will be yours. It is a gift for being the most powerful bloon defender of the whole Blooniverse. You will unlock a new mode: Fast Mode. You will repeat all over again but instead, all bloons are THRICE the speed as before. When Fast Forward, It will be 6 TIMES the speed as before, making it SUPER HARD, and also, you can't see TURBO because it travels as fast as the speed of light and when F.F. (Fast Forward), it goes 6x faster than the speed of light! Good thing you have the Stopwatch. The Stopwatch makes all bloons and blimps slow as a snail walking. Only in Fast Mode.
When you earn ALL THE MEDALS, you will get the "Super Fast Bloon Defender of the Whole Blooniverse Medal".
When you get that, you transfer to the track "Heaven, Hell, the God and the Devil" . You will defeat the NIATFG, the most powerful bloon in the whole Blooniverse!
When you do that, you just completed the WHOLE Bloons Tower Defense 6! Updates of more tracks and others will not deown you the two Special Medals.
This is a obvious reference! Here's the site to the reference: http://www.mariowiki.com/Star_Shrine