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