Here is the full list of all 25 RUSH achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Complete all hidden levels
Place a sign on every square of the credits level
Complete all actual challenge levels
Actually solve level garlic
Create a conveyor belt of 10 signs
Create an endless loop in a level using a conveyor
Create an endless loop in a level using two directional signs
Create an endless loop in a Hard level
Find all hidden levels
Find a hidden level
Complete all hard levels
Lead 1111 cubes to their exits
Create an endless loop in a level using a telewarp
Complete all medium levels
Deliver all presents in the eight levels when they are touched by frost in December
Find the hidden Toki Tori statue
Complete a level with signs to spare
Complete the Solar Flare level
Create an endless loop in a Medium level
Make 6 collisions at the same time
Create an endless loop in an Easy level
Complete all easy levels
Solve a level different from how the hint system suggests
Fail a level 15 times in a row
Complete all tutorial levels