This is the Guide for People who just miss one of them
Top 3 Easiest Achievement
3. Thinking WIth Portals
2. Welcome to Beach Island!
1. Speed Runner
100% Star Achievement
-Remember where you climb the tower of pipe thingy. After you got that star from there, Turn Around and Jump to the Left part of the platform and that way you can do some parkour way to find the star.
-There should be a Star within 2 Fans Where to part is Right Before you take the Rainbow Star from the Rock Platform, Go to the path from the Right Side and there should be there on your right, Also you might wanna Spam Shift and That way you can easily Get that star.
-There must be a Rainbow Star over by the Pipe as well, So you might jump down there from the north side around and you should just do a parkour There just to get a Star.
-It’s should be simple enough that where there was a Glass Platform, Go against that Purple stone wall thingy through the small sand path thingy just to get that star.
Once you start the game (Either Standard/Speedrun Mode)
Go to the Second Checkpoint and then you must do that parkour thing to your left like as by shown the picture below
And then it should be look like those type of easter egg thing, Touch it to get award.
Thanks to Redcat628 for his excellent guide, all credit to his effort. if this guide helps you, please support and rate it via Steam Community. enjoy the game.