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