Purple World
The Purple World is a world in 5b with weird stuff in it. Notable anomalies include: the HPRC, a purple ground (what is this, yoyleland?!), a whole Wood World and Factory World, level 29, zappy things, a secondary ground block which looks all retro like space alien game, a tree with a letter "I" dangling from it (who put it there?), recommended characters, and more which have yet to be discovered.
Secrets
Some say the original game was intended to have a comeback of the purple world for exactly 3 levels (2 transition levels and 1 fully purple level). It was going to be placed between the orange and pink worlds (orange juice and toothpaste? more research is needed.) as an additional anomaly to add to purple world's anomaly belt. Why place an old world in the middle of two new worlds? More research is needed (woah déja vü...)